OTTAWA -- The Canada Revenue Agency has launched an internal probe to determine how a late Mafia don who owed $1.5 million in back taxes received a refund cheque for more than $381,000.

Andrew Treusch, the agency's commissioner, says investigators from the security and internal affairs division are to report back by the end of the year, and their findings will be made public.

Treusch says the agency will immediately call in the police if the investigation uncovers possible criminal behaviour.

The statement follows a published report that the Canada Revenue Agency issued the refund to the now-deceased Nick Rizzuto despite his owing the taxman $1.5 million.

Rizzuto had just been arrested as part of a sweeping police operation in November 2006 and sent to prison. The elderly Mob boss was eventually released. He was murdered in his kitchen in 2010.

Enquete, an investigative program on Radio-Canada, says Rizzuto received a cheque dated Sept. 13, 2007, for more than $381,737.

Jean-Pierre Paquette, a former Canada Revenue Agency auditor, told the French-language CBC network that he told the Rizzuto family not to cash the cheque and even went to Rizzuto's home to retrieve it.