Winnipeg police are investigating how one of their shotguns was stolen and modified, then found in someone's home more than eight months later.

Officers found the shotgun along with several other firearms and some ammunition while responding to a child-welfare matter at a home in the Donwood Drive area on Monday.

The shotgun went missing from a marked cruiser on May 26, 2014, and had since been modified, police said in a news release Thursday.

A 28-year-old woman and 30-year-old man have been charged with numerous firearm-related offences. They were taken into custody.

Police have no answers as to how the shotgun was stolen or why the public was never notified.

"That's also forming part of that investigation. We're looking to see if there's, just the policies and procedures, with respect to that, the protocol was followed during the aspects of this," Winnipeg police Det. Sgt. Natalie Aitken said.

Since August, the police service requires all shotguns to be secured at the station when it's not signed out to an on-duty member, meaning firearms are no longer kept in cruiser cars.

All the service's firearms are currently accounted for, police say.