A gunman walked into a rear door at an alcohol detoxification center in Riverton and began shooting, killing one person and seriously injuring another, authorities said.

Witnesses described a chaotic scene Saturday in which the gunman went through the Center of Hope Alcohol Detoxification Center aiming at clients and firing shots, then left the building and surrendered to police.

Officers converging on the building around 4 p.m. surrounded a shirtless, heavyset man who held his hands in the air, the Riverton Ranger newspaper reported (http://tinyurl.com/ojvkupc ). Police didn't identify the man, and no motive has been released, but they said the suspected gunman is not affiliated with the detox center.

The injured man was in "pretty bad shape," police Capt. Eric Murphy said.

Police did not return phone calls Sunday seeking more details.

Police were called about a report of an "active shooter," and residents of the facility were told to hide in a bathroom to protect themselves, the Ranger reported.

One man told the newspaper the gunman tried to break into his room. The man said the shooter looked through a window at him, pointed his gun at him through the window, and attempted to open the door.

The unidentified man said the shooter wasn't able to open the door and he proceeded to another part of the building, armed with what the witness identified as a .45-caliber handgun. The witness said he saw shell casings on the floor outside his room.

After the shootings, authorities gathered the center's remaining occupants on the sidewalk across from the building. Many were upset, and several told the newspaper they would refuse to re-enter the center that night, even if it meant defying a court order.

The facility offers three days of close observation, 14 days of social detoxification, and up to three months of transitional living to its residents, including some people who are sent there by judges.

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Information from: The (Riverton, Wyo.) Ranger, http://www.dailyranger.com