The fourth person involved in a horrific accident in Vaughan that killed an off-duty York Region police officer and two others is in critical condition.

Mohammed Mattu, 19, of Vaughan, was taken to Sunnybrook Hospital Saturday morning after escaping the wreckage of a two-car crash near Woodbridge.

As of Sunday, he was on life support, suffering from massive brain injuries.

York Region police officers are mourning the loss of 28-year-old Const. Davis Ahlowalia who was described as a tireless humanitarian. He died after a minivan crossed the centre line on Major Mackenzie Drive near Pine Valley Drive and struck his car at about 3:30 a.m.

Flags were at half-mast at the police station in Newmarket where he was stationed.

The two other passengers in the van who died instantly were Vaughan residents Sulman Yusaf, 19, and Waleed Shaukat, 18.

Yusaf was at the wheel of the van when the accident occurred, CTV's Jim Junkin reported. The teens were out celebrating a birthday.

"I am feeling very sad, as the other fathers feel about their sons," said Yusaf's father, surrounded by grief-stricken family members.

Shaukat was loved by everyone in his community because he had a good heart, his brother said.

"Anybody that he talked to he touched because he was real," Omar Shaukat said.

Residents stopped by the crash site on Sunday and laid flowers.

"It's just terrible what happened here," one man told CTV News.

"It's a tragedy, in a sense," added another. "You had four innocent people basically going home from wherever they were."

The cause of the fiery crash has not yet been determined. The accident happened in heavy fog.

Ahlowalia, who often spent his vacation days in Jamaica and India helping poverty-stricken families, planned to travel to South America this year to help orphans and those with HIV/AIDS.

With a report from CTV's Jim Junkin