A fourth person has died as a result of injuries sustained in a multi-vehicle collision on Highway 401 in Ajax.
A 10-year-old boy succumbed to his injuries on Sunday, Ontario Provincial Police said.
The boy was injured in a pileup on the highway near Salem Road, at approximately 10:30 p.m. on Friday.
Police said traffic had either stopped or was slowing down due to construction in the area. A tractor trailer rear-ended one vehicle, causing an "extreme chain reaction" involving two other transport trucks and at least 16 other vehicles.
"The cars were just ripped open, like tin cans almost," OPP Sgt. Kerry Schmidt told reporters on scene.
"It was incredible the amount of damage that was sustained."
A man, woman and 12-year-old boy were also killed in the accident. OPP later said the 12-year-old and 10-year-old boys were brothers.
The adult victims’ neighbours of Pickering have identified the man killed in the crash as Carl Laws and the woman as Jackie Laws. They were just 10 kilometres away from home at the time of the accident.
Another 16 people were injured during the pileup, including five who were in critical condition on Saturday.
On Monday, Schmidt said four of the five were still in hospital, but only one was still in critical condition.
The fifth person who was in critical condition was the 10-year-old boy.
The driver of the transport truck was not injured.
The trucking company says it has launched an internal investigation and is co-operating with police.
Schmidt said no charges have been laid at this time and police continue to investigate the accident.
With a report from John Musselman
