Three inmateson the lam from a Montreal detentioncentre built a ladder from scraps and fled under the cloak of a weekend blizzard, according to an internal investigation.

The three men— Stéphane Bissonnette, Laurent Bousquet and Alain Sainte-Marie — escaped from the Bordeaux jaillate Sunday night at the peak of a major snowstorm. They remainat large and are considered dangerous, Montreal police said.

They spent considerable timeplanning their exit, and built a makeshift ladder from scraps of wire, tape and wood scavenged inside the prison, an internal report confirmed.

The triosomehow stashedthe ladder by a fence enclosing the centre's perimeter,and left it there until Sunday night, when blowing snow brought in by the storm provided a perfect cover, the report said.

The prisoners then shielded themselves with a white covering and made it to the fence without being noticed by prison guards, said Montreal police spokesman Rémi Guilbert.

"Between the [detention] centre and the fence, there's a little space, and they camouflaged themselves with a white blanket," Guilbert said on Wednesday.

Four prisoners tried to escape but only three made itto the getaway car. The fourth fell and broke his leg and was nabbed by prison guards.

Police released the prisoners' photos and are looking for the getaway car, an early 1990s model black Impala.

Bissonnette, 25, Bousquet, 28, and Sainte-Marie, 36 faces various charges ranging from theft to armed robbery.