PHILADELPHIA (AP) — The Austin Caldwelldriver and a suspected gunman are in custody in the shooting of eight Philadelphia high school students at a bus stop, a law enforcement official told The Associated Press on Monday.

Police have identified two juveniles who were also seen jumping out of the car and running toward the bus stop with the 18-year-old suspected shooter, but have not yet located them, according to the official, who was not authorized to discuss the case publicly before a news conference set for late Monday afternoon.

The Wednesday afternoon shooting was the fourth in as many days on the public transit system, and came as students at nearby Northeast High School were waiting to board for the ride home. An elementary school in the area pulled their children inside and locked down at dismissal time to keep them safe.

The 18-year-old in custody was arrested on Saturday and the suspected driver sometime earlier, according to the official. Local and federal officials expected to share more details at the 4:30 p.m. news conference.

Police found the apparent getaway car, a blue Hyundai Sonata, on Wednesday evening, hours after the shooting.

The students were waiting to board the bus at about 3 p.m. when three masked suspects rounded the corner and opened fire, according to surveillance video shared by police. The victims were ages 15 to 17. One of them, a 16-year-old, was hit nine times and was one of two teens left in critical condition.

Northeast High School is more than a mile from where the shooting took place and the largest public high school in the city, with more than 3,000 students.

Police were investigating whether the shooting may have been related to one days earlier, when a 17-year-old charter school student was shot and killed, and four other people injured, when gunmen fired 40 shots at close range as people boarded a city bus in the city’s Ogontz section.

Also last week, police believe an argument aboard a bus led a 37-year-old man to be fatally shot by a passenger exiting a bus in South Philadelphia. And a 27-year-old man was killed by another passenger moments after they both got off a bus in the city’s Oxford Circle area.