Howard County Police arrested a 17-year-old boy Tuesday in connection to the killing of a man last week.

The teenager, from Ellicott City, is charged as an adult with first-degree murder and related charges, according to police. He was arrested at 12:45 p.m. with a loaded gun in his backpack at Howard High School, where he is a student, police said.

“The suspect was under supervision of the Maryland Department of Juvenile Services and on an ankle monitor for a previous incident in another jurisdiction,” police said.

Detectives said a second, unidentified person is being sought.

Howard High School Principal Steven Fleming said in an email sent to the school’s community that the leadership team was aware of the police presence, and that the teen was immediately taken into custody in the front office.

“This is very troubling news, and I am sure students, staff, families, and community members are going to be very upset to learn of these events,” Fleming wrote. “I encourage students who might be upset to speak with a counselor or administrator at our school.”

Fleming said he and the school staff will monitor how the situation affects the school community and will provide more information as it becomes available.

The victim was 26-year-old Kendrick McLellan of Baltimore.

While making routine area checks, officers found McLellan at 2:14 a.m. Saturday, dead with multiple gunshot wounds in the driver’s seat of a vehicle, police said in a news release. The car was parked behind an office building in the 8800 block of Centre Park Drive in Columbia, a short distance from Howard High School.

Police determined that the shooting took place around 5 p.m. on Oct. 9, in the same location where police found him three days later.

Detectives believe that the victim and the teen were acquaintances, but the motive for the shooting is unclear.

Later that same day, two teens were found with nonfatal gunshot wounds on the same block. Police said they do not believe the shootings are related.

Around 9:10 p.m., police responded to the nonfatal shooting and found two boys, ages 16 and 17, from Elkridge, with gunshot wounds. They were taken to the University of Maryland Shock Trauma Center with non-life-threatening injuries.

Authorities said they believe that shooting occurred in the parking lot of the Columbia Palace Plaza shopping center.

Because the fatal and nonfatal shootings occurred less than a mile away from the high school, there will be an increased police presence in the area, said Seth Hoffman, public information officer for the Howard County Police Department. Officers will also do more area checks throughout the day.

He said the Police Department works with the school system any time there is an incident near a school that prompts increased patrols.

Police are asking anyone with information on the second person to contact police at 410-313-STOP or HCPDCrimeTips@howardcountymd.gov.

Correction: This story has been updated to correct the spelling of Steven Fleming’s surname.