The arson investigation into the massive wildfires in Slave Lake two years ago is over and no charges will be laid, CBC News has learned.

Fire ripped through the northern Alberta town in May 15, 2011, destroying more than 400 buildings and forcing 7,000 residents to flee their homes.

Officials said the fire, which resulted in about $700 million in damages and is considered the second costliest disaster in Canadian history, was likely caused by humans.

Today the RCMP said it has exhausted all leads and no more work will be done on the file unless new tips come in.

Twelve officers worked full-time and followed more than 250 leads, but found no evidence that would lead to criminal charges.

In late 2011, the Alberta government announced the fire was deliberately set and turned over its files and reports to the RCMP.

"Our investigation into the origin of that fire ruled out everything but arson as a probable cause," Frank Oberle, then Alberta's sustainable resource development minister, said at the time.

Oberle said the province knew precisely where the fire was set, but could not disclose the location as it was considered a crime scene.