LONG BEACH >> Police arrested an 18-year-old man Thursday on suspicion of fatally stabbing a Cabrillo High School student who was walking home from school Thursday afternoon.

Giovanny Montelongo, a Long Beach resident, was arrested within an hour of his alleged attack of Keshawn Brooks, who was 15 years old, Long Beach Police Chief Robert Luna said during a press conference that began shortly after 10 p.m. Thursday.

Luna was joined by grieving members of Brooks’ family during the press conference. The victim’s father, Keeyon Layton, implored any witnesses who may be able to help detectives solidify their investigation come forward with information.

• Video: Long Beach Police Chief Robert Luna explains detectives’ preliminary views on fatal stabbing

“My son was not a gang member. This was a murder, done outright, and he did not deserve this,” Layton said, choking back tears. “And to the people who came to his aid, I would like to thank you very much. It pleases me that he was not alone during his time of death.”

Police responded to the assault, which Luna said “makes no sense,” at about 3:25 p.m. in the 2800 block of Santa Fe Avenue in West Long Beach near Stephens Middle School.

As of Thursday night, Luna said investigators have not yet come to a firm conclusion that robbery was the motive behind the fatal assault of Brooks, but Montelongo first attacked Brooks by grabbing the teenager’s backpack.

• Video: Vice Mayor Suja Lowenthal speaks at press conference

“During the confrontation, the suspect stabbed Keshawn and ran from the location,” Luna said.

Police arrived on the seen two minutes after being dispatched, Luna said. Long Beach Fire Department paramedics took Brooks to a hospital, where he died from his wounds.

Officers tracked the suspect to a location in the 1700 block of West Columbia Avenue, near where the stabbing took place, and made the arrest.

The heavy police response happened around the same time students at Stephens Middle School were being dismissed from class.

Luna expressed gratitude to witnesses who called 911 and administered first aid to Brooks. He said police arrested Montelongo within an hour of the attack, and credited the quickness of officers’ finding their suspect to good police work and cooperation from community members.

Luna also said to prevent future scuffles from becoming homicides, police need the public to call them at first signs of trouble.

“When you see a fight, when you see something going on — when you see something, say something,” he said.

City Councilwoman Suja Lowenthal, who spoke at the start of the press conference, asked the city to keep the family of the victim “in your hearts and hold them dear” in the midst of this “senseless act of violence.”

“When a child is lost to one of us, he is lost to all of us,” Lowenthal said.

Contact Andrew Edwards at 562-499-1274.