The 2005 Mayerthorpe RCMP Murders

The investigation at the farm

On March 2, 2005, RCMP officers attended a rural property near Mayerthorpe, Alberta, while a court-ordered property seizure was being carried out. Police obtained evidence supporting a search warrant for a marijuana grow operation, and members remained at the property overnight while investigators also prepared to examine suspected stolen vehicles and parts.

Early the next morning, officers were securing a Quonset hut on the property. The RCMP later identified the four constables killed there as Peter Christopher Schiemann, 25; Anthony Fitzgerald Orion Gordon, 28; Lionide Nicholas Johnston, 32, commonly known as Leo; and Brock Warren Myrol, 29.

The shooting

At about 9:15 a.m. on March 3, members of the Edmonton RCMP Auto Theft Unit arrived and heard gunfire from inside the Quonset hut. A man emerged and fired at the arriving officers, who returned fire. The suspect retreated into the building. When police later secured the scene, the four constables and the suspect were found dead.

The gunman was identified as property owner James Roszko. The RCMP concluded that Roszko fatally shot the four officers before taking his own life after being wounded during the exchange with another officer. The killings became the deadliest single-day loss of life for the RCMP in its history at that time.

How Roszko returned to the property

The later criminal cases focused on the help Roszko received before returning to the farm. Shawn Hennessey and his brother-in-law Dennis Cheeseman admitted that they supplied Roszko with a rifle and gave him a ride back toward the property during the night before the shootings.

That legal distinction matters. Roszko was the gunman who killed the four constables. Hennessey and Cheeseman were not convicted of murder. Each pleaded guilty in 2009 to four counts of manslaughter based on the assistance they provided to Roszko before the ambush.

Sentences and appeals

The sentencing judge imposed headline terms of 15 years for Hennessey and 12 years for Cheeseman, then credited their guilty pleas and time already spent in custody. Their remaining custodial terms were reported as approximately 10 years and four months for Hennessey and seven years and two months for Cheeseman.

Both men appealed for shorter sentences. The Alberta Court of Appeal rejected those efforts, and in August 2011 the Supreme Court of Canada declined to hear a further sentence appeal. Their manslaughter convictions therefore remained in force.

Later release history

Cheeseman reached statutory release in 2013 after serving the legally required portion of his sentence. Hennessey was later granted day parole and then full parole in 2015. His sentence expired in 2019. Those release decisions concerned sentence administration; they did not erase the manslaughter convictions.

Institutional aftermath

The deaths prompted extensive examination of police safety. A federal workplace-safety investigation led the RCMP to issue enhanced body armour intended to provide greater protection from long-gun threats. A memorial park in Mayerthorpe was later dedicated to the four officers.

Current status

The identity of the gunman and the criminal responsibility established against Hennessey and Cheeseman are no longer unresolved. Crime by Region therefore classifies the case as Solved / Adjudicated. The page does not describe Hennessey or Cheeseman as convicted murderers because their convictions were for manslaughter.