John Lee Cowell, 27, was arrested on Monday at the Pleasant Hill BART Station after a rider called the police alerting them he was on a train, according to BART officials. The Alameda County District Attorney’s Office charged Cowell on Monday with the murder of 18-year-old Nia Wilson and the attempted murder of her sister.

According to BART officials, Wilson and her sister were standing on the MacArthur BART Station platform waiting for a train on Sunday when Cowell came up from behind and fatally stabbed her. According to the Oakland Police Department, the attacks were unprovoked.

More than 1,000 people gathered on Monday to celebrate the life of Wilson near the BART Station where she was killed. Family members played some of her music for the crowd, Wilson was a rapper.

BART Police, who made the arrest, described Cowell as calm when he was arrested. The deputy chief of BART Police, Ed Alvarez, said he was sitting down in a car and had no weapons in his possession. BART Police said now they are tracing Cowell’s steps from the time the crime was committed to his arrest. Cowell had a court date set for 2 p.m. in Oakland.