Police say they’ve arrested a 66-year-old homeless man for fatally stabbing a 72-year-old victim inside a Metro car in downtown Long Beach last week.

At about 5 a.m. on April 1, a train operator called 911 for help after spotting the victim lying on the Metro station platform on Pacific Avenue near Fifth Street, according to Long Beach police and a Metro spokesperson.

The victim was taken to a hospital, where he succumbed to his injuries on Monday, police said. He was identified as 72-year-old James Plummer, of South Gate.

On Thursday morning, officers arrested 66-year-old Cary Odell Singletary near Pacific Avenue and First Street on suspicion of stabbing Plummer.

Investigators are still looking into what sparked the stabbing, but they do not believe Singletary and Plummer knew each other.

A search warrant police filed the same day as the stabbing revealed how police tracked Singletary down.

Police wrote that security camera video from inside the Metro car showed a man stabbing Plummer before exiting the car and fleeing in an unknown direction. They did not provide any further description of the attack or what led up to it.

Through other security camera footage, detectives tracked the assailant’s movements from before he boarded the Metro at Willow Street Station, near the intersection of Willow Street and Long Beach Boulevard.

Detectives said they canvassed the area near Willow Street Station and found out that the man had left Long Beach Memorial Hospital shortly before getting on the train. They filed the search warrant to get his name and other identifying information from the hospital.

Singletary was being held on $1 million bail and was scheduled to be arraigned on murder charges on Wednesday afternoon.