ASPEN, Colo. (AP) _ The fatal injuries Michael Kennedy suffered when he hit a tree while skiing New Year's Eve were ``instantaneous and incapacitating,'' according to an autopsy report released Sunday.

Two sets of drug tests found no trace of alcohol, amphetamines, barbiturates, marijuana, cocaine or opium in Kennedy's system, the report said.

The 39-year-old son of the late Sen. Robert F. Kennedy fractured his skull and cervical vertebrae and severed his spinal cord, according to the report released Sunday by Rob Kurtzman, the coroner who performed the autopsy.

``Injuries were instantaneous and incapacitating and death was in seconds to minutes,'' the report said. A laceration on top of Kennedy's head was a half inch long.

Pitkin County Deputy Coroner Tom Walsh said even if Kennedy had survived the head-on crash into the tree on Aspen Mountain, he would have been paralyzed from the shoulder down.

Walsh said a helmet might have helped Kennedy survive the impact, but it would not have protected him from the spinal and neck injuries suffered in the crash.

Kennedy also suffered several nonfatal injuries _ including a fractured right wrist, according to the report.

The fatal accident occurred while Kennedy was playing a football game on skis with about 20 other people on Aspen Mountain, witnesses told investigators.

Pitkin County Sheriff's Investigator Dave Blaine said rules of the game required a skier to hold onto the ball for no more than five seconds before passing it.

Witnesses told Blaine that Kennedy had caught a pass and was looking over his right shoulder for someone to throw the ball to when he hit the tree.

Kennedy's death has been ruled an accident and the coroner's case is now closed, Blaine said.