Four days. Four crime scenes. Nine bodies.

In the same week as one of the worst killing sprees in Aurora's history, three people were found tied up and shot to death in an apartment Thursday, just two miles from the scene where six people were gunned down on Labor Day.The explosion of violence left police with one youth in custody and three gunmen on the loose.

"I've been here 25 years, and I've never seen a run like this," said Mike Stiers, the deputy police chief in Colorado's third-largest city.

Police spokesman Bob Stef said two men and one woman were killed in Thursday's shootings, while another woman was taken to University Hospital in Denver, where she was in critical condition with multiple gunshot wounds. All four were thought to be in their late teens or 20s.

The shootings were reported about 7 p.m., and witnesses told police they saw three men running from The Trails apartment complex. It appeared the attackers had not acted at random, police said.

The recent killings - which police believe are not related - have been especially brutal, with point-blank shotgun blasts and people bound and shot to death.

And the number of homicides in this sprawling city of 250,000 adjoining Denver keeps climbing, from 11 in 1996 to 17 last year. This year the number stands at 21, with more than three months to go.

Police searched for motives in both attacks and were working to build a case against the Aurora teenager accused in Monday's kill-ings.

Police allege Alexander Pogosyan, 17, and Michael Martinez, 18, killed four friends and one victim's mother on Labor Day at two different homes.

At the Trails complex, people cried and hugged each other as police worked.

A man who identified himself as the father of a victim moaned and held his head in his hands. He said three people lived in the apartment and that all were students.

"I want to know what this world is coming to," said Krys Thompson, a resident of the gated complex. "It scares me. I swear, it scares me."