A 21-year-old man was arrested for investigation of first-degree murder after a veteran Denver policewoman who was raising her 12-year-old daughter alone was shot and killed during a free jazz festival, police said Monday.

Suspect Rollen Oliver was taken into custody late Sunday after witnesses gave a description of the gunman. Police also recovered a gun and said they believe Oliver was the only person involved in the attack.

Police Chief Robert White said investigators were not sure if Officer Celena Hollis was the target of the shooting when she answered a call about a disturbance in the park.

"There was a tragic event last night and a beautiful young, single mother and a valuable member of the Denver Police Department lost her life," Public Safety Manager Alex Martinez said.

Authorities said they did not know the cause of the disturbance.

Oliver appeared in court Monday and was ordered held without bond. District attorney's spokeswoman Lynn Kimbrough said a decision on charges was not expected until later this week.

Oliver was escorted into the courtroom by six deputies, all wearing black and blue bands of mourning over their badges.

Oliver wore a red jail jumpsuit and had chains around his waist that were held by a deputy, according to the Denver Post (http://bit.ly/Lld3Bx).

Hollis was in uniform and off-duty when she was shot in the head and later died at a hospital.

Hollis was a Detroit police officer before she joined the Denver Police Department in 2005. She also served as president of the Denver Police Department Black Police Officers Organization.

The park remained closed while police searched for more evidence.

At least three shots were fired Sunday shortly after a jazz band finished playing on a lake-side pavilion stage. Concert-goers scattered during the shooting.

More than 1,000 people were at the City Park Jazz concert, the fourth of 10 shows scheduled for this summer in the annual series that draws families and others to one of the city's more popular summer events. The mayor said late Sunday the concerts should continue.

"We will not surrender what we consider special in this city to anyone," Mayor Michael Hancock said.

Nakira Doss, a jazz singer, said she hopes the series continues.

The 28-year-old mother was at the show Sunday and sitting near the stage with her children, ages 4, 5 and 7, when she heard at least two shots. As people ran past, she told her children to get on the ground before she laid over them.

"I'm trying to show them music, but at what cost," she said, nodding toward her children.

City Park sprawls across several hundred acres east of downtown. It's also the site of the Denver Zoo and Museum of Nature and Science, as well as ponds, trails and recreational fields.

After shots rang out, scores of people ran from the northwest side of the pond and stage area, confusing crowds on the south side of the pond that were still lingering over conversation and picnics in lawn chairs and blankets.

Someone announced from a loudspeaker on stage that the park was closed and told park goers to leave from the south side.

Samuel Bell, 19, of Denver said he was looking for a space for his scooter in the parking and heard several shots.

"We just arrived at the park. It was crowded, it was looking fun," Bell said. "And then 'pa-pa-pa-pa' outta nowhere.

"We just ducked," Bell said. "We pulled off in enough time to get away. It was crazy."

He estimated he was about 10 to 20 feet from the spot where the officer was shot.