Two Alberta men have been charged with first-degree murder in the 2005 fatal shootings of four Mounties near Mayerthorpe in northern Alberta, police said Sunday.

Pictured here are Const. Tony Gordon, top left, Const. Leo Johnston, top right; bottom left is Const. Brock Myrol and bottom right is Const. Peter Schiemann. All died in the March 2005 shootings.
(RCMP)

Dennis Keegan Rodney Cheeseman, 23, and Shawn William Hennesey, 28, both from Barrhead, were each charged with four counts of first-degree murder following a 28-month investigation, police said at a news conference.

RCMP Deputy Commissioner Bill Sweeney, who held the news conference at Mayerthorpe's memorial to the fallen officers at police headquarters, said the charges were "the first significant update" in the investigation of the killings, a crime that he described as "the darkest day in RCMP history."

RCMP Cpl. Wayne Oakes told CBC News that the two men are accused of being a party to the offence for aiding and abetting gunman James Roszko, who ambushed the four RCMP officers on March 3, 2005, in the force's biggest single-day loss in more than 100 years.

Cheeseman and Hennesey, who are in custody in Edmonton, are to appear in Mayerthorpe provincial court Thursday, police said.

Roszko, a virulent cop hater, later killed himself on his farm near Mayerthorpe, which is 130 kilometres northwest of Edmonton.

"Today, those charges were sworn before the courts, bringing to a conclusion a very lengthy and challenging investigation," Oakes said.

Oakes declined to provide further details about how the men allegedly helped Roszko, saying that would be discussing evidence which is now before the courts. But he said that it's not believed they were on the property at the time of the shootings. 

The families of the Mounties have been contacted by police, and most of them have requested that their privacy be respected, Oakes said.

After the end of the news conference, Grace Johnston, mother of Const. Leo Johnston, said after months of anguish she is heartened by the arrests.

"This is awesome that maybe now we will get some answers," she said, choking back tears in a phone interview.

Dozens of investigators involved

To date, the investigation has cost $2 million and involved as many as 200 investigators and support staff, police said. Up to 40 officers and staff are now working on the case. Sweeney would not say if more arrests are possible.

Cheeseman and Hennesey, who are brothers-in-law and lived together at the time of the killings, were known to police and were well acquainted with Roszko, RCMP Assistant Commissioner Rod Knecht said.

"They were associates over an extended period of time," he said.

Roszko killed the four officers who were at his Rochfort Bridge farm investigating his property, which was believed to have been the site of an auto chop shop and a marijuana grow-op. 

Earlier this year, the RCMP completed a report on worksite safety issues stemming from the Mayerthorpe shootings and submitted it to the federal Human Resources and Social Development Department.

That report recommended that RCMP in Alberta be supplied with enhanced body armour and review its portable radio communications capability and coverage. It also recommended that night vision equipment be issued to officers working nights.

All three recommendations are being addressed, RCMP said.

Alberta's Justice Department is to call a fatality inquiry into the circumstances of the deaths of constables Peter Schiemann, Tony Gordon, Brock Myrol and Johnston. No date for that inquiry has been set.

With files from the Canadian Press