Two rival motorcycle clubs were "possibly" involved in the violence at the Colorado Motorcycle Expo, police Chief Robert White said at a press conference.
The Denver Post quoted a witness
, who didn't want to be identified because of fear of retaliation, as saying the violence involved rival biker gangs. Video taken after the shooting showed police talking to groups of men wearing jackets with motorcycle club patches.
White said about 10,000 people were inside the National Western Complex hall at 12:45 p.m. (2:45 p.m. ET) when shots were fired.
Investigators think two or more people exchanged gunfire, he said, but the cause of the shooting is still being investigated.
One person was fatally shot and three were wounded by gunfire, White said. One person was stabbed and three other people suffered injuries probably caused in a fight, but not by weapons, he said.
No arrests have been made but people are being questioned.
"Whether it was motorcycle gang-related or motorcycle club-related, that is yet to be determined," the chief said.
Sunday motorcycle expo canceled
The 38th annual expo for Sunday has been canceled, according to the city, but the Arenacross event will go on Saturday night and Sunday afternoon at the National Western Complex. Arenacross has no relation to the expo, the release said.
People who were inside the hall said the violence happened quickly.
Britney Shaw, who was working at a jewelry stand, told the Post she saw a group of about 50 men brawling on the stairs, which were covered in blood and cordoned off.
Bob Cook, who was running a booth for leather goods, told the Post
he heard shots and saw people dive under tables. He didn't know what caused the shooting but said that minutes later the scene returned to normal despite puddles of blood on the floor.
White was asked whether any law enforcement officers were members of the motorcycle clubs at the expo. White said he didn't know. He said, however, "There were no Denver police officers involved."
The Saturday expo continued after the shooting. When asked why it wasn't shut down immediately, White said authorities thought the scene was safe because of the heavy police presence and because most people had vacated the building.
Hospital locked down after shooting
Authorities provided slightly different numbers of injured people.
White said seven people were injured. Earlier in the day, a Denver Health Medical Center doctor said six people were hurt, with three in critical condition and three in stable condition. Before that, Denver Health had tweeted
that nine people had been taken to area hospitals.
As a safety precaution, the hospital emergency department at the hospital was locked down until about 4:30 p.m. (6:30 p.m. ET), according to a medical center tweet.
"We wanted to make sure the incident didn't spread from the expo to the hospital," White said.
The complex is near the Denver Coliseum. Police initially tweeted that the incident occurred at the coliseum.