Updated

The 30 people missing after a runaway train crash in Quebec over the weekend are presumed dead, police said Wednesday, in what has become Canada's worst railway catastrophe in almost 150 years

"We informed them of the potential loss of their loved ones," Quebec police inspector Michel Forget said Wednesday after meeting with families of the dead and missing. "You have to understand that it's a very emotional moment."

With 20 bodies found in Lac-Megantic so far, that would put the death toll from Saturday's derailment and explosions at 50. Some of the bodies may never be found, as authorities believe several victims were vaporized in the intense heat.

Quebec Premier Pauline Marois arrived Thursday to tour the site.

"The leader of this company should have been there from the beginning," Marois said at a news conference.

Attention focused on Edward Burkhardt, the CEO of Montreal, Maine & Atlantic Railway, the train's U.S.-based parent company, who faced jeers from residents when he visited the town Wednesday for the first time since the disaster. He blamed the train's engineer for improperly setting its brakes before it derailed.

Burkhardt said the train's engineer had been suspended without pay and was under "police control."

The unmanned train hurtled down a seven-mile incline, derailed and ignited in the center of Lac-Megantic early Saturday. All but one of its 73 cars was carrying oil, and at least five exploded.

The intensity of the explosions and fire made parts of the devastated town too hot and dangerous to enter and find bodies days after the disaster. Only one body had been formally identified, said Genevieve Guilbault of the coroner's office, and she described efforts to identify the other remains as "very long and arduous work."

Burkhardt, president and CEO of the railway's parent company, Rail World Inc., was expected to meet with residents and the mayor of the town Thursday.

Investigators also had spoken with Burkhardt during his visit, said a police official, Sgt. Benoit Richard. He did not elaborate.

Until Wednesday, the railway company had defended its employees' actions, but that changed abruptly as Burkhardt singled out the engineer.

"We think he applied some hand brakes, but the question is, did he apply enough of them?" Burkhardt said. "He said he applied 11 hand brakes. We think that's not true. Initially we believed him, but now we don't."

Burkhardt did not name the engineer, though the company had previously identified the employee as Tom Harding of Quebec. Harding has not spoken publicly since the crash.

"He's not in jail, but police have talked about prosecuting him," Burkhardt said. "I understand exactly why the police are considering criminal charges ... If that's the case, let the chips fall where they may."

Investigators are also looking at a fire on the same train just hours before the disaster. A fire official has said the train's power was shut down as standard operating procedure, meaning the train's air brakes would have been disabled. In that case, hand brakes on individual train cars would have been needed.

The derailment is Canada's worst railway disaster since a train plunged into a Quebec river in 1864, killing 99.

Quebec police have said they were pursuing a wide-ranging criminal investigation, extending to the possibilities of criminal negligence and some sort of tampering with the train before the crash. The heart of the town's central business district is being treated as a crime scene and remained cordoned off by police tape.

At a news conference shortly before Burkhardt's arrival, Marois faulted his company's response.

"We have realized there are serious gaps from the railway company from not having been there and not communicating with the public," Marois said. She depicted Burkhardt's attitude as "deplorable" and "unacceptable."

Burkhardt, who arrived in town with a police escort, said he had delayed his visit in order to deal with the crisis from his office in Chicago, saying he was better able to communicate from there with insurers and officials in different places.

"I understand the extreme anger," he said. "We owe an abject apology to the people in this town."

In an exchange with reporters, Burkhardt defended the practice of leaving trains unmanned, as was the case when the train rolled away. Canadian transportation department officials have said there are no regulations against it.

"For the future we, and I think probably the rest of the industry, aren't going to be leaving these trains unmanned," Burkhardt said. "We'll take the lead with that. I think the rest of the industry is going to follow."

Among the residents looking on as Burkhardt spoke was Raymond Lafontaine, who is believed to have lost a son, two daughters-in-law and an employee in the disaster.

"That man, I feel pity for him," Lafontaine said. "Maybe some who know him properly may think he's the greatest guy in the world, but with his actions, the wait that took place, it doesn't look good."

The disaster forced about 2,000 of the town's 6,000 residents from their homes, but most have been allowed to return.

Transportation Safety Board investigator Donald Ross said the locomotive's black box has been recovered, and the fire and the chain of events that followed are a "focal point" of the investigation.

The accident has thrown a spotlight on MMA's safety record. Before the Lac-Megantic accident, the company had 34 derailments since 2003, five of them resulting in damage of more than $100,000, according to the U.S. Federal Railroad Administration.

Burkhardt said the figures were misleading.

"This is the only significant mainline derailment this company has had in the last 10 years. We've had, like most railroads, a number of smallish incidents, usually involving accidents in yard trackage and industry trackage," he told the CBC.

Nonetheless, Burkhardt predicted the accident would lead to changes in the way railways operate, and indicated that MMA would no longer leave loaded trains unattended, a practice he said was standard in the industry.

"We want to cooperate with the town and help the residents in getting them back on their feet," Burkhardt said. "We're accepting claims that they have for their loss and ensuring nothing like this would ever happen again."

The tanker cars involved in the crash were the DOT-111 type -- a staple of the American freight rail fleet whose flaws have been noted as far back as a 1991 safety study. Experts say the DOT-111's steel shell is so thin that it is prone to puncture in an accident, potentially spilling cargo that can catch fire, explode or contaminate the environment.

The derailment also raised questions about the safety of Canada's growing practice of transporting oil by train, and is sure to bolster the case for a proposed oil pipeline running from Canada across the U.S. -- a project that Canadian officials badly want.

The oil on the runaway train was being transported from North Dakota's Bakken oil region to a refinery in New Brunswick on Canada's East Coast. Because of limited pipeline capacity in the Bakken region and in Canada, oil producers are increasingly using railroads to transport oil to refineries.

In Washington, White House spokesman Jay Carney said President Barack Obama's administration was closely monitoring the aftermath of the accident, and has offered assistance to Canadian officials. He said firefighters and firefighting vehicles were deployed from Maine to assist with the response, and got help from U.S. customs and border agents in making the trip.

The Associated Press contributed to this report.