TORONTO - The locomotive from a deadly train derailment was destined for a secure holding facility Tuesday where investigators could pore over the wreckage as they work to uncover the cause of the tragedy.

The twisted and crushed steel of the massive engine car was the last piece to be removed from the crash site west of Toronto, where three engineers were killed and 45 passengers injured when the Via passenger train careened off the tracks Sunday.

The Transportation Safety Board refused to comment on the progress of their investigation Tuesday, but have said the black box would be key in the search for answers. The train's speed, the brake pressure, when the brakes were applied, and whether the whistle was blowing can all be ascertained from the data held in the device.

Via reported that train operations in the area had returned to normal by late Tuesday afternoon.

"The trains are back on the track today," said Via spokeswoman Michelle Lamarche.

Halton police reported Tuesday that they had accounted for all 75 passengers who were on the train. Some were not injured and left the scene Sunday on their own.

Forty-five passengers were admitted to hospital for injuries ranging from minor to a broken leg, a back injury and a heart attack after the locomotive and one passenger car flipped onto their sides and crashed into a small building next to the tracks. Another passenger car was leaning precariously in the aftermath, and three other cars were vacant.

All but eight passengers had been discharged from hospital by Monday, and another passenger was reported to have been discharged Tuesday.

A lawsuit was launched Tuesday on behalf of the passengers by Toronto firm Falconer Charney and Sutts, Strosberg LLP of Windsor, Ont. -- the same firm that argued a successful class action in a 1999 Via accident in Thamesville, Ont.

Two engineers died in that crash after a train jumped the tracks and plowed into parked freight cars.

"In a case like this, if we're successful, people would be compensated for personal injury, psychological injury, lost income, lost belongings," said lawyer Sharon Strosberg.

The lawsuit was filed on behalf of one person, but Strosberg said she expected to add more passengers Wednesday.

Although investigators have refused to speculate on the possible cause of the crash, they had said the train was switching tracks when it derailed.

The speed limit for a passenger train along that corridor is about 80 mph, or 130 kilometres per hour, except when it's changing tracks. Then the speed limit drops to 15 mph, or 24 kilometres per hour.

Faisal Abid, a Toronto entrepreneur sitting near the front of the first car, said Tuesday that he felt the train "wasn't going as fast as normal, but it was still going fast."

"It was really crazy," Abid said. "I was just trying to hold on and stay in my seat."

CN, which owns the tracks and leases them to Via, has also said it investigated the tracks before the crash and found no signs of deterioration or wear.

Police remained at the scene of the accident to help with security Tuesday, but were no longer involved in the investigation since there's been no indication of a criminal element to the derailment.

Three locomotive engineers were killed in the crash, including Peter Snarr, 52, and Ken Simmonds, 56, two experienced drivers, each with more than 30 years in the industry.

A trainee, Patrick Robinson, 40, of Cornwall, Ont., joined them in the cab to observe, though investigators haven't ruled out the possibility that he was driving at some point. Although Robinson was new to passenger trains, he had 20 years experience with freight.