A 15-year-old was taken into custody as police continue to search for a second suspect after three people were killed, and four others were wounded Sunday in a mass shooting at the Seattle Center, according to Mayor Katie Wilson and police.

"We believe this teenager opened fire in the crowd, but details are still under investigation," Wilson said. 

No homicide charges have been filed against the teen, who was booked into juvenile detention on suspicion of firearms violations and first-degree assault, Wilson said. The juvenile was expected to make an initial court appearance Monday.

Seattle Police Department Chief Shon Barnes said investigators believe two individuals exchanged gunfire outside the Seattle Center Armory, leaving multiple bystanders caught in the crossfire.

Police believe the shooting stemmed from a conflict between two small groups or gangs.

An active manhunt remains underway for the second suspected shooter. However, police acknowledged it is technically possible that one of the fatally shot victims was the second gunman, though that has not been confirmed.

Officials said a 19-year-old man and a 44-year-old man died at the scene despite life-saving efforts by first responders. 

A 56-year-old woman was also transported to a local hospital in critical condition, where she later died. 

Four other victims were injured, including a 2-year-old boy, a 23-year-old man, a 39-year-old woman and a 40-year-old woman. Officials said the toddler, who was initially transported to the hospital in stable condition, has since been upgraded to satisfactory condition. The remaining victims either suffered minor injuries or had already been discharged from the hospital.

Police are also investigating whether a 27-year-old man who self-transported to a hospital was an eighth victim. His involvement has not yet been confirmed.

"Everyone was just throwing stuff and running," Carris told The Seattle Times. "Like everyone."

Todd Behrends, 59, said he heard what appeared to be several rounds of shots.

People began running and jumping over each other to escape, Behrends told the outlet. One woman fell, and someone stepped on her leg.

Behrends said he saw a woman on the ground and a man on a stretcher as he ran toward an exit.