Campus Alert Archive
Mt. SAC

One person stabbed during an altercation in a campus building; suspect arrested

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CAstabbingemergency notificationmedium confidence
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Confirmed Threat

On the morning of Wednesday, September 20, 2023, a physical altercation in Building 26B at Mt. San Antonio College escalated into a stabbing at approximately 11:30 AM PDT, with the victim suffering torso and neck wounds. The campus-wide Mt. SAC Alert was sent at roughly 12:10 PM PDT, about 40 minutes after the attack, a gap that drew criticism from students and faculty over the college's emergency notification practices throughout the fall. Suspect Gavin Flores, 18, was arrested on suspicion of attempted murder; classes in Buildings 26A, 26B, and 26D were canceled for the rest of the day.

Alerts
1
Response
—
Killed
0
Injured
1
Institution
Mt. San Antonio College
Community College · CA
All Mt. SAC cases →
~55,000 studentsRaveMt. SAC Alert
Documented Timeline

Alert Sequence

1 message in sequence · 1 verified verbatim

INITIAL ALERTSMS
Verified verbatimSAC Media (Mt. SAC student newspaper), which published the verbatim Mt. SAC Alert in its fall 2023 campus-safety investigation156 chars
MtSAC Alert: An altercation resulted in a physical attack at about 11:40 am. Police investigating. Suspect in custody. Witnesses please call (909) 274-4555.
Reports the incident as occurring 'at about 11:40 am' (Mt. SAC's own timestamp); the LA County Sheriff's Department logged the 911 call at approximately 11:30 AM PDT, so the alert's stated time differs by about 10 minutes from the logged call time
The alert went out approximately 40 minutes after the incident; Professor Shiloh Blacksher, who was on scene, raised the lag at the September 21 Academic Senate meeting along with concerns about construction obstructing EMS access and trauma-counselor response time
The message uses present tense ('Police investigating', 'Suspect in custody') because by the time the alert went out, the suspect was already in custody; the alert was less a warning than a notification
The alert did not instruct students in Building 26 to evacuate while the second-floor scene in 26B was still being processed
Mt. SAC primarily uses Rave-based SMS and email; the same message was simultaneously posted to the college's main Facebook and X accounts
Message elements

How the first alert is built

To check this alert, Claude (an AI) read it in full 25 separate times, independently. Each read decided whether the message answers each of the six questions and gave a short reason. A final reviewer then weighed all 25 and wrote the plain-English verdict you see when you open a row. The score (for example 22/25) is how many reads agreed; the 25 individual reads are tucked underneath if you want to check them.

MtSAC Alert: An altercation resulted in a physical attack at about 11:40 am. Police investigating. Suspect in custody. Witnesses please call (909) 274-4555.

  • Sourcepresent25/25

    Final assessment

    Unanimous: it opens with the branded MtSAC Alert signature and names Police, identifying the sender.

    Who is sending the alert and who is responding. People act faster on a message from a clearly identifiable, credible sender, such as a named department, the police, or a branded alert system, than on an anonymous notice. A branded signature counts.

    See all 25 individual reads
    1. present: Opens with branded signature "MtSAC Alert" and names "Police".
    2. present: It opens "MtSAC Alert", a branded sender tag.
    3. present: Branded "MtSAC Alert" signature identifies the college as sender.
    4. present: The branded tag "MtSAC Alert" and "Police investigating" identify sender and authority.
    5. present: Opens with branded signature "MtSAC Alert" and references "Police".
    6. present: It opens with "MtSAC Alert" and names "Police investigating", identifying the sender.
    7. present: The branded "MtSAC Alert" tag and "Police" identify the sender and responder.
    8. present: Opens with the branded signature "MtSAC Alert" and references "Police".
    9. present: Branded "MtSAC Alert" and references "Police investigating".
    10. present: It opens with the branded "MtSAC Alert" signature identifying the sender.
    11. present: The branded "MtSAC Alert" plus "Police" identify the sender.
    12. present: Branded signature "MtSAC Alert" identifies the sender.
    13. present: Opens with branded tag "MtSAC Alert", identifying the sender.
    14. present: The branded signature "MtSAC Alert" identifies the sender.
    15. present: The branded "MtSAC Alert" tag identifies the sending alert system.
    16. present: Opens with branded "MtSAC Alert" and names "Police investigating".
    17. present: The "MtSAC Alert" signature and "Police investigating" identify the sender.
    18. present: It opens with the branded signature "MtSAC Alert", identifying the sender.
    19. present: It opens with the branded signature "MtSAC Alert" and references "Police".
    20. present: It opens with the branded signature "MtSAC Alert", identifying the sender.
    21. present: Opens with the branded signature "MtSAC Alert", identifying the sender.
    22. present: Opens with branded signature "MtSAC Alert" and names "Police".
    23. present: The branded "MtSAC Alert" tag and "Police" identify the sender.
    24. present: The branded "MtSAC Alert" tag and "Police" identify the sender.
    25. present: The branded "MtSAC Alert" signature and "Police" identify the sender.
  • Hazardpresent25/25

    Final assessment

    Unanimous: it names a physical attack, a specific assault hazard.

    What the threat actually is. A complete warning names the specific danger, such as a shooter, a fire, a tornado, or a gas leak, rather than a vague emergency, because people decide what to do based on what they are facing.

    See all 25 individual reads
    1. present: Names "a physical attack", a specific assault hazard.
    2. present: It names "a physical attack", a specific threat.
    3. present: Names "a physical attack" / altercation, a specific assault.
    4. present: It names "a physical attack", a specific threat.
    5. present: States "a physical attack", with suspect in custody, a specific threat.
    6. present: It names "a physical attack" from "An altercation", a specific threat.
    7. present: It states "a physical attack", a specific threat.
    8. present: States "An altercation resulted in a physical attack", a specific threat.
    9. present: States "a physical attack", a specific threat.
    10. present: It names "a physical attack", a specific threat.
    11. present: It states "a physical attack", a specific assault.
    12. present: Names "a physical attack", a specific hazard.
    13. present: States "a physical attack", a specific threat.
    14. present: It states "a physical attack" requiring police, a specific hazard.
    15. present: It names "A physical attack", a specific threat.
    16. present: Names "a physical attack", a specific threat.
    17. present: It names "a physical attack", a specific threat.
    18. present: It names "a physical attack", a specific threat (a stabbing altercation).
    19. present: It reports "a physical attack", a specific threat.
    20. present: It states "a physical attack" with police investigating, a specific named threat.
    21. present: States "a physical attack", a specific threat.
    22. present: Names "a physical attack", a specific threat.
    23. present: It names "a physical attack" from "An altercation", a specific threat.
    24. present: It names "a physical attack", a specific threat.
    25. present: It names "a physical attack", a specific offense.
  • Locationabsent0/25

    Final assessment

    Unanimous: no building, street, or campus location is stated, so location is absent.

    Where the threat is. Saying whether danger is in a specific building, a part of campus, or area-wide lets people judge their own proximity and choose a safe direction. Without a where, a warning is hard to act on precisely.

    See all 25 individual reads
    1. absent: No building, street, or campus location is stated in the text.
    2. absent: No building, area, or "campus" location is stated in the text.
    3. absent: No building, street, named place, or "campus" location is given.
    4. absent: No building, street, area, or campus location of the attack is named in the text.
    5. absent: No building, street, area, or campus location is stated beyond the alert tag.
    6. absent: The text names no building, area, or campus location for the attack.
    7. absent: It names no building, street, area, or campus location in the text.
    8. absent: No building, street, area, or "campus" location of the attack is stated in the text.
    9. absent: No building, street, or campus area is named.
    10. absent: It states no building, street, or campus location.
    11. absent: No building, hall, street, or campus area is named in the text.
    12. absent: No building, street, or place is named, only the alert signature.
    13. absent: No building, street, or campus location is named in the text.
    14. absent: It gives no building, street, or campus area where the attack occurred.
    15. absent: No building, street, area, or "campus" location is named in the text.
    16. absent: No building, street, or campus area is named in the text.
    17. absent: It names no building, street, area, or campus location for the attack.
    18. absent: It names no building, street, or place, only "Police investigating" generally.
    19. absent: No building, street, or campus area is named in the text.
    20. absent: It names no building, area, or campus location for the attack.
    21. absent: No building, street, area, or "campus" location is given in the text.
    22. absent: The text gives no building, area, or place where the attack occurred.
    23. absent: No specific building, street, or campus location is named in the text.
    24. absent: No building, area, or campus location is stated in the text.
    25. absent: No building, street, area, or campus location is named beyond the branded tag.
  • Guidancepresent25/25

    Final assessment

    Unanimous: it asks witnesses to call a police number, a requested action to recipients.

    The protective action to take. A clear, specific instruction, such as shelter in place, evacuate, avoid the area, or run-hide-fight, drives faster and more correct protective behavior than describing the threat alone.

    See all 25 individual reads
    1. present: Asks "Witnesses please call (909) 274-4555", a requested action.
    2. present: It instructs "Witnesses please call (909) 274-4555", a directed action.
    3. present: Asks "Witnesses please call (909) 274-4555", a directed action.
    4. present: It instructs "Witnesses please call (909) 274-4555", an instruction to recipients.
    5. present: Instructs "Witnesses please call (909) 274-4555", an instruction to recipients.
    6. present: It instructs "Witnesses please call (909) 274-4555".
    7. present: It instructs "Witnesses please call (909) 274-4555", an action request.
    8. present: Asks "Witnesses please call (909) 274-4555", a requested action.
    9. present: Instructs "Witnesses please call (909) 274-4555".
    10. present: It instructs "Witnesses please call (909) 274-4555".
    11. present: It asks "Witnesses please call (909) 274-4555", a directive to recipients.
    12. present: Asks "Witnesses please call (909) 274-4555".
    13. present: Instructs "Witnesses please call (909) 274-4555", an instruction to recipients.
    14. present: It instructs "Witnesses please call (909) 274-4555".
    15. present: It instructs "Witnesses please call (909) 274-4555", an action for recipients.
    16. present: Asks "Witnesses please call (909) 274-4555", a directive to recipients.
    17. present: It instructs "Witnesses please call (909) 274-4555".
    18. present: It instructs witnesses to "please call (909) 274-4555", a requested action.
    19. present: It directs "Witnesses please call (909) 274-4555", a directed action.
    20. present: It asks "Witnesses please call (909) 274-4555", an instruction to recipients.
    21. present: Asks "Witnesses please call (909) 274-4555", a directive to recipients.
    22. present: Instructs "Witnesses please call (909) 274-4555".
    23. present: It asks "Witnesses please call (909) 274-4555", an instruction to recipients.
    24. present: It asks "Witnesses please call (909) 274-4555".
    25. present: It instructs "Witnesses please call (909) 274-4555".
  • Timepresent25/25

    Final assessment

    Unanimous: it gives about 11:40 am, a specific time.

    When the message applies. A timestamp, the word now or immediately, or a phrase like until further notice tells the reader whether the danger is current and how quickly to act.

    See all 25 individual reads
    1. present: Gives "at about 11:40 am".
    2. present: It says the attack was "at about 11:40 am", a clock time.
    3. present: Gives "at about 11:40 am", a clock time.
    4. present: It states "at about 11:40 am", a clock time.
    5. present: Says "at about 11:40 am", a clock time.
    6. present: It gives "at about 11:40 am", a clock time.
    7. present: It gives "at about 11:40 am", a clock time.
    8. present: Says "at about 11:40 am", a clock time.
    9. present: Gives "at about 11:40 am".
    10. present: It says the attack was "at about 11:40 am", a clock time.
    11. present: It gives "at about 11:40 am".
    12. present: Gives "at about 11:40 am".
    13. present: Gives "at about 11:40 am", a clock time.
    14. present: It provides "at about 11:40 am".
    15. present: It states the attack was "at about 11:40 am", a clock time conveying when.
    16. present: Gives "at about 11:40 am".
    17. present: It says it occurred "at about 11:40 am", a specific time.
    18. present: It gives the recency reference "at about 11:40 am".
    19. present: It gives "at about 11:40 am", a clock time.
    20. present: It says it occurred "at about 11:40 am", a clock time.
    21. present: Says it occurred "at about 11:40 am", a clock time.
    22. present: Gives "at about 11:40 am".
    23. present: It cites "at about 11:40 am".
    24. present: It gives "at about 11:40 am", a clock-time cue.
    25. present: It gives "at about 11:40 am", a clock time.
  • Impactpresent25/25

    Final assessment

    Present by unanimous agreement; a physical attack resulting from an altercation conveys a stated harm to a person.

    What the hazard could do to the people in its path. Beyond naming the threat, a complete warning conveys its potential consequences or severity, such as that a tornado can level buildings or that a leak could be explosive, so recipients grasp how much danger they are in. Research on warning message content finds that a concrete impact statement helps people personalize their risk and act sooner.

    See all 25 individual reads
    1. present: It reports a physical attack resulting from an altercation, a stated harm to people.
    2. present: Reports an altercation that resulted in a physical attack, a stated harm to people.
    3. present: States an altercation resulted in a physical attack, a stated harm to a person.
    4. present: Describes a physical attack resulting from an altercation, a stated harm to a person.
    5. present: It reports an altercation that resulted in a physical attack, stating actual harm to someone.
    6. present: It states an altercation resulted in a physical attack, a stated harm to a person.
    7. present: Describes an altercation resulting in a physical attack, a clearly stated harm to a person.
    8. present: Reports an altercation that resulted in a physical attack, a stated harm to a person.
    9. present: Describes a physical attack from an altercation, a stated harm to a person.
    10. present: The text reports an altercation that resulted in a physical attack, a stated harm to a person.
    11. present: It reports an altercation that resulted in a physical attack, a stated harm to people.
    12. present: States an altercation resulted in a physical attack, a clearly stated harm to a person.
    13. present: It reports a physical attack from an altercation, a stated harm to a person.
    14. present: Reports an altercation that resulted in a physical attack, a stated harm to a person.
    15. present: It reports a physical attack from an altercation, a stated harm to a person.
    16. present: Reports a physical attack from an altercation, an explicit stated harm to a person.
    17. present: Reports an altercation that resulted in a physical attack, a stated harm to a person.
    18. present: It reports a physical attack from an altercation, a stated harm to a person.
    19. present: It reports a physical attack resulting from an altercation, a clear harm to a person.
    20. present: Reports a physical attack resulting from an altercation, a stated harm to a person.
    21. present: It reports a physical attack from an altercation, a stated harm to a person.
    22. present: It reports a physical attack resulting from an altercation, a stated harm to a person.
    23. present: Reports a physical attack resulting from an altercation, a stated harm to people.
    24. present: Reports a physical attack from an altercation, a stated harm to a person.
    25. present: States an altercation resulted in a physical attack, a stated harm to people.

Systematic AI judgments with visible reasoning, not human-validated codings.

About this analysis
Context

Background

Mt. San Antonio College is the largest single-campus community college in California, serving roughly 55,000 students annually at its 421-acre campus in Walnut, eastern Los Angeles County. The September 20, 2023 stabbing began as an altercation over a female student between her current boyfriend and an ex-boyfriend, all three of whom were Mt. SAC students. According to LASD, the ex-boyfriend (Gavin Flores, 18, of West Covina) was the aggressor and pulled a knife, stabbing the female student's current boyfriend multiple times in the torso and neck on the second floor of Building 26B at 1100 N. Grand Avenue; the female student had previously reported Flores to Mt. SAC's Title IX office and police for harassment and stalking and was in the process of filing a restraining order against him. The 18-year-old suspect, Gavin Flores of West Covina, was taken into custody on suspicion of attempted murder and held on $1 million bail; charges were later reduced and he pled no contest to a misdemeanor violation of Penal Code § 626.10 for one year of summary probation. Much of the subsequent campus discussion focused on the Mt. SAC Alert response time. The campus-wide text alert went out roughly 40 minutes after the incident, did not instruct anyone in Building 26 to evacuate while the scene was still active, and timestamped the attack at '11:40 am', about 10 minutes later than the LASD-logged incident time. Faculty and students raised the issue at the September 21 Academic Senate meeting, and the lag became the focal point of a fall-long campus-safety discussion that included concerns from the Deaf and hard-of-hearing community about whether they could rely on the alert system, questions about construction obstructing EMS access, and complaints about trauma-counselor response time. By April 2024, Mt. SAC committed to installing additional cameras in response to the cluster of fall 2023 incidents, which also included two sexual assaults, a knife-point robbery, and a separate parking-lot attack. The case documents a notification that arrived after the actual threat had already been neutralized, the operational counterpart to false-positive cases such as swatting.
Analysis

Key Findings

Roughly 40 minutes elapsed between the stabbing and the campus-wide alert, which reported the suspect already in custody; faculty raised the lag at the September 21 Academic Senate meeting
The alert's own timestamp ('at about 11:40 am') differs by about 10 minutes from the LA County Sheriff's logged incident time (approximately 11:30 AM PDT)
The alert did not instruct students in Building 26 to evacuate; the crime scene was still being processed on the second floor while the building remained occupied
The incident prompted a fall-long campus-safety discussion at Mt. SAC, including concerns from ACCESS and the Deaf/hard-of-hearing community about whether SMS-only alerts adequately served them
Outcome
Victim hospitalized with stab wounds to torso and neck; survived. Suspect Gavin Flores, 18, of West Covina, arrested on suspicion of attempted murder and held on $1 million bail; on October 1, charges were reduced: Flores ultimately pled no contest to a misdemeanor violation of Penal Code § 626.10 (weapons on school grounds) for one year of summary probation, 15 days of community labor, and search/seizure plus weapons conditions. Classes in Buildings 26A, 26B, and 26D canceled for the rest of Wednesday; campus reopened Thursday.
Provenance

Sources

  1. Student Paper
    Altercation between three people leads to stabbing at Mt. SAC - SAC Media
    sac.media
    archived copy
  2. Student Paper
    Is Mt. SAC safe? - SAC Media (fall 2023 campus-safety investigation)
    sac.media
    archived copy
  3. Student Paper
    Update on Mt. SAC stabbing incident - SAC Media
    sac.media
    archived copy
  4. News
    Student stabbed at Mt. San Antonio College in Walnut; suspect arrested - ABC7 Los Angeles
    abc7.com
    archived copy
  5. News
    Altercation over female student leads to stabbing at Mt. San Antonio College - KTLA
    ktla.com
    archived copy
  6. Student Paper
    Mt. SAC installing cameras amid continuing safety concerns - SAC Media
    sac.media
    archived copy
Cite this case

Campus Alert Archive. "Mt. San Antonio College: One person stabbed during an altercation in a campus building; suspect arrested." Incident of September 20, 2023. Added May 2026; last updated July 2026. https://campusalertarchive.com/case/mt-san-antonio-college-stabbing-2023-09-20/

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Alert text quoted on this page remains the work of the issuing institution; the archive is a secondary source.

Tags
community-collegestabbingmt-saccaliforniaresponse-time-lagclery-actattempted-murderwalnutaccessibility-concernsdelayed-alert
Added May 2026Updated July 2026Via ingestion