A government report released Thursday said six violent prisoners escaped from a Canadian jail last summer after spending four months digging an escape route with nail clippers and other makeshift tools.

The report, which examined how the prisoners broke out of the Regina Provincial Correctional Centre last August, said the men toiled away at their escape plan while dozens of workers failed to see what was happening.

The investigating team "accepts that an inmate or a group of inmates can deceive a corrections worker on a particular shift; but cannot accept that an entire corridor of inmates can deceive at least 87 different corrections workers ... and engineer an escape of this magnitude," the report said.

The prisoners, four of whom faced murder charges, dug the hole using a modified nail clipper to remove the grill on a heating register. With other makeshift tools they removed the steel backplate of the register and exposed the exterior brick wall. Then they chipped away at the brick until they could smash through the wall.

The report said other inmates distracted corrections staff while the digging was taking place by playing cards in the corridor and blocking the view. A video camera in the corridor didn't cover the area.

Once through the wall, the men used ropes braided out of blankets to scale the compound wall and winter coats as protective covering to climb over razor wire fencing.

The inmates who escaped were being held on several serious charges, including murder. One was recaptured almost immediately, but it took weeks to track down the other five.

Investigators said that staff was tipped about a possible escape two months earlier, but did not do enough to follow up on the information.

In response to the report's 23 recommendations, the Saskatchewan government has announced plans to build a new remand center in Saskatoon. The government said the four-year, $67 million project will be built with security measures appropriate for remanded inmates accused of violent crimes.

The prisoners themselves seemed surprised that their caper succeeded.

"We didn't think we would get away with it," one escaped prisoner told the investigating team.

"We started working on it. It was something to do and we just kept at it. When we didn't get caught, we picked our night and just went."