As towering flames lit the night sky in the early morning of July 6, 2013, employees of the now-defunct Montreal, Maine and Atlantic (MMA) railway spoke to each other with growing apprehension, trying to figure out the cause of the blazing inferno which was ravaging downtown Lac-Mégantic.

"The town of Lac-Mégantic is on fire, from the church to the Metro to the river," MMA locomotive engineer Tom Harding is heard saying on audio recordings played to Superior Court Justice Gaétan Dumas and the jury in a Sherbrooke courtroom Wednesday.

"The flames are 200 feet high," Harding tells rail traffic controller Richard Labrie.

Labrie, 59, and Harding, 56, along with former MMA operations manager Jean Demaître, 53, are on trial for criminal negligence causing 47 deaths in connection with that tragedy.

"It's not us," Labrie says in an earlier conversation to Demaître. "We have a train in Nantes and in Vachon."

"It might be the gas line that blew up," he surmises.

Tom Harding calls MMA railway traffic controller Richard Labrie to describe the fire at Lac-Mégantic. The locomotive engineer doesn't yet know it's his runaway train. 0:48

Realization slowly dawns

After about an hour after the initial call, Labrie suggests to Demaître the possibility that the MMA fuel train might be to blame.

"Stop that," replies Demaître, using a French cuss word.

"What I want to know is if it's our train that ran down," says Labrie. "It's stressing the hell out of me."

Demaître then asks if Harding secured his train.

"Yes," says Labrie.

"I f--king hope it's someone else's fault, not ours," says Demaître.

'There is no more downtown'

Around 2:30 a.m. ET, a taxi dispatcher from Lac-Mégantic calls Labrie, informing him it's MMA's 74-car fuel train, parked 12 kilometres away at Nantes, which has rolled into downtown Lac-Mégantic, derailed and burst into a raging blaze.

"It's burning like hell, man," says the dispatcher. "There is no more downtown, Richard."

"Calisse," swears Labrie, breathing heavily. "Oh no."

Warning: Explicit language in the audio that follows:

Lac-Mégantic taxi dispatcher calls rail traffic controller Richard Labrie and confirms MMA's 74-car fuel train has rolled into downtown Lac-Mégantic and exploded. 0:59

"Dozens and dozens of people are going to die," says the taxi dispatcher.

Labrie is then heard calling Demaître.

"Put on your pants," he tells him. "The train ran down."

"You're kidding me?" says Demaître.

"The train ran down. We're in deep shit, tabarnak," says Demaître. "[Harding] didn't secure it properly."

Harding finds out it's his train

Sometime after 2:30 a.m., Harding calls Labrie from a payphone to get an update.

Labrie tells him it was the fuel train he'd left in Nantes which is burning in Lac-Mégantic.

"No. no. F--k, Tabarnak de tabarnak. It was secure when I left," Harding says. "[Richard], it was secure."

Labrie asks Harding how many handbrakes he applied to the rail cars.

Seven, Harding tells him.

Warning: explicit language in the audio that follows:

Tom Harding learns from rail traffic controller Richard Labrie that the train that derailed and exploded in downtown Lac-Mégantic is the one he left on the track at Nantes. 0:50

Several conversations later, Harding calls Labrie back from the gas station where he's been waiting, asking what he should do and where he should go.

Labrie tells him he's not sure.

"I don't feel too good right now," Harding tells Labrie.

"I understand," replies Labrie. "Me neither, I don't feel good."

"I can't believe the damage in downtown Mégantic," continues Harding.

"I can't imagine, maybe because I don't want to imagine. I guess it must be f--king hell" says Labrie.

"It is," Harding replies.

Number of handbrakes called into question

In one of the last audio recordings heard by the jury, MMA's former assistant director, Michael Horan, asks Labrie what happened.

Labrie tells him about the initial fire on the locomotive left idling in Nantes the night before, explaining that firefighters had put it out and turned off the engine.

Horan tells Labrie he should have told them to leave the locomotive running.

Labrie is then asked how many handbrakes Harding left on the train. Labrie counts out the handbrakes, for a total of seven.

"Tabarnak, that's not enough," Horan responds.

Worst thing imaginable

The rail traffic controller who took over Labrie's duties later that day told the court that he had no idea what had happened when he got to the train station at Farnham, 65 kilometres southeast of Montreal.

That moment my life changed forever. — Steve Jacques, rail traffic controller

Steve Jacques, the 25th witness to testify in the trial, described the first few minutes of his workday.

"[Labrie is] someone who's very orderly,'' Jacques said. "But I arrived and there were papers everywhere."

Jacques said he tried to make a joke, but Labrie was busy on the phone, so he started working.

Jacques said when he asked Labrie what was going on, Labrie responded by asking him what was the worst thing he could imagine happening.

He responded: "We go to Montreal, and the drawbridge goes up, and a fuel train derails into the seaway."

"I still hadn't seen [Labrie's] face," Jacques added. "He was green. He said, 'Mégantic is on fire.'"

Jacques asked Labrie if he meant the railyard in Mégantic, he testified.

"No," Labrie told him. "The town is on fire."

"I was in shock," Jacques told the court.

"I went on [the] internet and saw the video that everyone else saw, and at that moment my life changed forever."

Jacques is expected to continue his testimony Thursday.