AURORA, Colo. (AP) _ Jacob Tilley recalls 18-year-old Michael Martinez as a scrawny kid who liked to play the tough guy.

Tilley, just a year older, attended the same high school as Martinez. He said the other teen would menace others yet never followed through on his threats.

``I think most of it is just wannabe stuff,'' Tilley said. ``Nobody took him seriously.''

Residents in this Denver suburb now take him very seriously. Police say Martinez and an accomplice launched a killing spree Monday that left five people dead in two homes.

Hours later, Martinez's own bullet-ridden body was found lying in a field near an upscale shopping mall, about 10 miles from the crime scenes.

The surviving suspect, a 17-year-old whose name was not released by police, was charged Tuesday with six counts of first-degree murder.

All six victims and the suspect knew each other, police said. But authorities were unsure what triggered one of the worst multiple slayings ever in this sprawling suburb.

``The motive is really the $64,000 question,'' police spokesman Bob Stef said. ``We don't know if it was out of anger, revenge, involving someone else.''

Police said Martinez and the 17-year-old suspect donned bandanas to conceal their faces Monday afternoon and stormed into a townhouse, killing two young men with shotgun blasts.

One victim was identified by police as Eddie Morales Jr. Friends identified the other as Zach Obert. Both were 18.

After the slayings, police said, Martinez and his companion traveled six blocks to a two-story home and shot Penny Medla, in her 30s, her stepson, Greg, 18, and his girlfriend, Marissa Avalos, 16. Mrs. Medla's 6-year-old daughter and 9-year-old son escaped unhurt.

Acting on a tip, police found Martinez's body late Monday. He had been shot several times with a handgun. The 17-year-old suspect was arrested 15 hours after the killings. No weapons have been recovered.

Police were sorting out the chain of events and attempting link the victims to the slayings. Authorities said that several victims attended nearby Overland High School.

``We have been able to put together that they are all acquaintances of each other, that they have had common interests; that they have run together in the past,'' said Deputy Police Chief Mike Stiers.

The brutality of the crime sent a shiver of fear through residents of Aurora, some of whom were told to stay indoors for about five hours while police SWAT teams hunted for the fugitives.

The shootings brought back memories of a bloody 1993 rampage that left four dead in a Chuck E Cheese restaurant in this same suburb.

Outside the apartment complex she shared with Martinez, Mary Johnson watched her small son splash in a puddle of water in the parking lot.

``It's frightening,'' she said. ``I want to get away from here. I don't feel comfortable anymore.''