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Tuesday update: Police have arrested a 30-year-old man in connection with Mario Fierro’s killing.

SAN DIEGO — A popular high school teacher was shot and killed in the North Park neighborhood early Monday.

Cathedral Catholic High School canceled classes after San Diego police informed them their teacher, Mario Fierro, was found dead in a suspected homicide.

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Mario Fierro taught social science at Cathedral Catholic High School.
Photo: Aida Bustos, Diocese of San Diego

Officers with the San Diego Police Department were called to an area near 4500 Kansas Street in North Park around 7:10 a.m. They found a 37-year-old man with a bullet wound unresponsive on the sidewalk. Officers said he died at the scene despite life-saving efforts.

The trunk of Fierro’s car was ajar, a sign he was headed to CCHS to start his work day. A witness told detectives Fierro may have been involved in an altercation with a Latino man in his 40s, who was said to be wearing jeans and a zip-up top. The suspect was last seen northbound on Kansas Street in a small, older car.

The Diocese of San Diego said Fierro graduated from CCHS/University High School in 2002 and came back to teach social science in 2016. He also served as athletic director at Notre Dame Academy. A social media post by CCHS congratulated him on his engagement to another teacher in December.

A fundraiser started to help with Fierro’s funeral costs had already raised more than $10,000 less than 12 hours after his death.

“Everyone in our school community mourns his loss. Mario was young, vibrant and full of life. All of us loved him. He was a fantastic teacher and a great human being,” a school email to parents and staff said.

A vigil was planned for 7 p.m. at St Therese of Carmel Catholic Church, and extra security was expected on CCHS campus and in the surrounding area as police search for Fierro’s killer.

The school said grief counseling will be available for students, faculty and staff.

Check back for updates on this developing story.