Dwain Lingenfelter was chosen as the new leader of the Saskatchewan NDP on Saturday. (Stefani Langenegger/CBC)

A membership scandal within the Saskatchewan New Democratic Party will be the focus of a criminal investigation, the RCMP announced Thursday.

Police had been looking into a complaint of forgery from a resident of a First Nation in the Meadow Lake area of Saskatchewan. During the provincial party's leadership race, supporters of Dwain Lingenfelter — who went on to win the contest — submitted 1,100 membership application forms, using names of people from reserves around Meadow Lake.

The forms were rejected when it was determined they were not sent in by the people named on the applications. Instead, an internal examination found that a Lingenfelter campaign worker had amassed the names and the paperwork, on his own initiative.

The RCMP said on Monday that they had received a verbal complaint alleging forgery. They said at the time they would look into the matter to determine if a criminal investigation was warranted.

Deb McDonald, CEO of the party, told CBC News that members would cooperate fully with the police investigation.

The NDP's political rivals, the governing Saskatchewan Party, issued a statement through a spokeswoman Thursday afternoon.

"We are confident the RCMP will do a thorough investigation and take appropriate action," Kathy Young, executive director of communications for the provincial cabinet, said in a news release. "Today's announcement suggests that the investigation undertaken by the NDP did not go far enough in getting to the truth of this very important matter."

The RCMP were tight-lipped about their investigation and declined to answer questions seeking more details.