Durham Regional Police are trying to piece together what happened at a serious motor vehicle accident and stabbing in Ajax that they believe might be related.

"It's a real whodunnit in terms of the group down at the station under arrest," Sgt. Nancy Van Rooy of Durham police told ctvtoronto.ca on Friday evening.

This occurred in the area of Griffiths Drive and Leah Crescent at 12:45 p.m., she said.

That location is several blocks north of Highway 2.

"There are two people who have been struck by a motor vehicle and have been seriously injured," she said.

One of those individuals were airlifted to hospital in Toronto. That person has life-threatening injuries. A second person from the accident scene has serious but non-life-threatening injuries, Van Rooy said.

Meanwhile, a stabbing in a nearby park left a third person with non-life-threatening injuries.

Van Rooy said a mobile command centre and traffic services specialists were at the scene. Homicide investigators are on standby in case one of the victims dies.

"Well, the injuries (in the MVA) are very serious," she said.

Van Rooy said police suspect that the stabbing and the MVA are related. "It's all in the same vicinity and at the same period in time," she said.

A precautionary lockdown had been issued for two local high schools while suspects were at large, but it was lifted shortly after 2:15 p.m.

Meanwhile, police have some work to do in determining exactly what happened.

"We do have conflicting information as to whether or not persons that were injured inside the vehicle or whether they were on the roadway and struck by the vehicle," Van Rooy told CTV Toronto.

Police later stopped another vehicle at Highway 2 and Brock Road, taking some young men into custody. Those individuals are believed connected to the accident and stabbing.

Van Rooy would only say that police have between three and five people in custody. Some are being detained for interviews, but others are under arrest.

However, she said "there's no talk yet" on what charges the arrested individuals might be facing.

With a report from CTV Toronto's Austin Delaney