In an interview with police, he admitted he was waiting in the driver's seat of the Jeep as other associates were committing a burglary, according to court documents.
A source familiar with the case said the officer's body camera video gives a clear view of her standing in street as the vehicle comes at her.
In December, she won the "Officer of the Month" award for the Parkville precinct.
The officer, who was identified as Amy Caprio in the probable cause statement, was pronounced dead after being rushed to a hospital. A Maryland prosecutor said the 16-year-old suspect is being charged with murder and treated as an adult.
The records don't list an attorney for Harris, and attempts to reach people believed to be his family members were not immediately successful. The school was released around 7:15 p.m.
An intense manhunt was underway Tuesday morning for the three additional suspects, authorities said.
"This tragedy is a solemn reminder of the sacrifice our police and public safety personnel make and are prepared to make to keep us safe each and every day", said Baltimore County Councilman Julian Jones. He was scheduled to appear before a judge at a Towson courthouse at 1 p.m. Tuesday.
She is the tenth Baltimore County officer to die in the line of duty, and the department's first female officer to die in the line of duty. The police tweet did not explain the delay in announcing the teen's apprehension.
It is unknown at this time if the officer fired her weapon during the confrontation, Vinson said.
Harris also told the detective that he "drove at the officer", the statement said.
Trump 'demands' probe into whether Federal Bureau of Investigation infiltrated his campaign
The president later wrote that if the allegations were true, it would be the "all time biggest political scandal! ". The department noted that a USA attorney would be consulted if evidence of criminal conduct was found.
Heavily armed Maryland police working with dogs had searched through the night for the other three suspects. Police said he is awaiting a bail hearing.
Officials initially said there were four possible suspects at large who were believed to be "armed and unsafe".
He says police from several agencies backed by federal law enforcement are widely searching the area for "multiple suspects" who are possibly armed.
Investigators urged residents in a sizable swath of Perry Hall to stay hunkered down inside their homes and lock all doors and windows as officers searched the community fringed with woodlands.
'The suspect who committed this awful crime remains at large, and @MDSP are assisting Baltimore County Police in their search.
A Baltimore County police spokesman says the officer had responded to a call just before 2 p.m. about a suspicious vehicle.
"The dark will not hamper our investigation", he told reporters Monday evening, adding the suspects' Jeep was ditched on a road and had been recovered.
Tony Kurek told The Associated Press his adult son was outside in the family's yard Monday afternoon in the northeast Baltimore County community when the son saw the officer with her gun drawn, confronting the occupants of a Jeep. The police officer has not been identified.
"They actually saw a black Jeep Wrangler and they saw that I guess it was a dead end street and they went to turn around and officers were following them". An officer has been injured and taken to a local hospital.