An unattended train rolled down an incline into Lac-Megantic, Que., on July 6, exploding into fireballs and killing at least 15 and leaving 35 missing. Here is a timeline of some key events leading up to the accident:

11 p.m. ET (July 5) -- Eastbound train with five locomotive units and 72 tank cars carrying crude oil stops at Nantes, Que. The train is operated by the Montreal, Maine and Atlantic Railway.

11:50 p.m. -- A fire in a parked locomotive is reported to the rail-traffic controller. Firefighters and an employee of the Montreal, Maine and Atlantic Railway -- not the engineer -- arrive on site. The engineer had retired for the night.

Midnight -- The fire is extinguished and the engine is shut down. The Transportation Safety Board at a news conference Tuesday would not say who shut down the engine or who was last inside the train, key points as the rail company has said the shut down "may have resulted in the release of air brakes on the locomotive that was holding the train in place." Nantes fire department has said it shut off the engine in order to fight the blaze, and says that's the proper procedure as spelled out by the railway company. The railway suggested the fire department should have called the engineer to the scene before leaving.

12:56 a.m. ET (July 6) -- After the fire crew and the employee of the Montreal, Maine and Atlantic Railway depart, the train starts to move. It begins rolling down the slope away from Nantes and toward Lac-Megantic about 10 kilometres away. Train picks up considerable speed, well beyond the normal limit.

1:14 a.m. -- Train derails in Lac-Megantic. The locomotive detaches and continues through town for about a kilometre. Residents report a series of explosions, with fireballs shooting into the sky and a wall of flames pounding the town. The downtown core is eviscerated, with a bustling bar, the library, and a cherished waterside park among the dozens of structures destroyed.

(Based on information from Transportation Safety Board and interviews with Nantes Fire Department and Montreal, Maine and Atlantic Railway)