Police asked for the public's help Saturday in the search for a missing shotgun thought to have ended the life of Cold Spring police officer Tom Decker, as investigators tried to piece together the sequence of events that led to the shooting and answer remaining questions about Decker's suspected killer.

In a release Saturday afternoon, the Stearns County Sheriff's Office confirmed that a 20-gauge shotgun is the weapon believed used in Decker's slaying and asked Cold Spring residents to check yards and other areas around their homes.

Decker, 31, was shot and killed behind Winners Sports Bar on Main Street late Thursday during an ambush as he and his partner responded to a report of a suicidal person.

Within an hour of the shooting, police arrested Ryan Michael Larson, 34, in his apartment above the bar. But the events that took place in those minutes remain unclear, including what happened to the gun.

Larson remained in custody in the Stearns County jail Saturday, and authorities offered few new details about the case, other than to say the investigation is continuing. Several members of Larson's family declined to comment.

Questions also hovered over Larson's recent past. Public records indicate he had lived at several addresses in the St. Cloud area before moving to Cold Spring, where he rented an apartment above Winners bar. According to court records, he faced eviction in 2008 by a St. Cloud property management company for failing to pay rent.

Dml - Special To The Star Tribune, Star Tribune
A banner in support of the police department made by students and staff at St. Boniface School hangs outside of the library in Cold Spring after the death of officer Tom Decker December 1, 2012.

In 2009, an ex-girlfriend requested a protective order after she said he got angry and aggressive, charging and spitting at her and bruising her arm, according to court documents.

At the time of the shooting, Larson was filling in as a bartender at Winners while attending St. Cloud Technical and Community College, where he was studying to be a machinist, according to one of the bar owners.

Police have located several guns belonging to Larson. He held a permit to carry a handgun, according to Jeff Scoles, a friend and co-owner of the bar where Larson worked. But an employee of the Del-Tone/Luth Gun Range said he had never seen Larson at the St. Cloud facility.

Residents were warned to call 911 and not to touch a gun if they found it. Anyone with information about the shooting is asked to call the Stearns County Sheriff's Office at 320-251-4240.

Decker's funeral will be at 11 a.m. Wednesday at St. John's Abbey and University Church in Collegeville. Visitation will be at 4 p.m. Tuesday at St. Boniface Catholic Church in Cold Spring.