GREENWICH, Conn. – A key witness in the murder case against Kennedy nephew Michael Skakel has died in Rochester, N.Y., apparently from tainted drugs, police said.

Gregory Coleman, who attended a substance abuse program in Maine with Skakel, testified that Skakel once told him: “I’m gonna get away with murder. I’m a Kennedy.”

But Coleman also admitted during a hearing in April that he was under the influence of heroin when he testified before a one-judge grand jury about the case.

Rochester police spokeswoman Sgt. Cheryl Franks said Coleman was the sixth area drug addict to die in the past week from a batch of bad drugs. Police were unsure whether the tainted drugs were heroin, crack or powder cocaine or some combination of the three, she said.

Skakel’s defense lawyer, Michael Sherman, called the death “not terribly surprising.” He said Skakel, who has had his own struggles with addiction, looks upon Coleman’s death as “a very sad event.”

Prosecutors could not immediately be reached for comment Wednesday evening.

The state had been expected to rely heavily on Coleman’s testimony that Skakel admitted killing 15-year-old Martha Moxley in 1975, when they were neighbors in the exclusive Greenwich enclave of Belle Haven.

Moxley was beaten to death with a golf club that was later matched to a set owned by the Skakel family.

Several years later, Coleman and Skakel were classmates at the Elan School in Poland Springs, Maine. Coleman and another former student have testified in pretrial proceedings that Skakel admitted killing Moxley the night of Oct. 30, 1975. Skakel was also 15 at the time.

No arrests were made for more than 24 years. Skakel was charged in the killing in January 2000 and later arraigned as a juvenile. A juvenile court judge ruled in January that Skakel should be tried as an adult and found that reasonable cause existed to try Skakel.

A second hearing was required after the case was transferred to adult court. It was during that proceeding that Coleman stunned the courtroom by admitting he had been high when he testified to the grand jury.

Sherman had asked Coleman why he told the grand jury Skakel discussed the murder five or six times but later said it was only one or two times.

“I was on drugs when I came before the grand jury,” Coleman answered.

Coleman also testified that he used crack cocaine and heroin before a television interview on the case in Rochester.

“Are you on drugs now?” Sherman asked.

No, Coleman replied. “Give me a urine test,” he added.

“No thanks,” Sherman said, drawing laughter from the courtroom but a reprimand from the judge.

Coleman went on to describe his own life filled with alcoholism, drug addiction, a criminal record and homelessness; at times he was living under a bridge.

Another former classmate, John Higgins, testified that Skakel told him of the killing during a tearful confession on the front porch of a dormitory while the two served as night guards.

“He related to me at some point prior to being there, there was a murder and that he was somehow involved in it,” Higgins said.

He described a drawn-out confession in which Skakel initially said he did not know if he committed the murder.

“He eventually stated that ‘I must have done it’ and eventually stated, ‘I did it,”‘ Higgins said.

But Higgins admitted he lied to investigators when they first asked him about the alleged confession. He also admitted asking about a $50,000 reward in the case.

Two other Elan students testified for the defense that they never heard Skakel confess.

Joseph Ricci, the founder of the Elan School, had also insisted that Skakel never made any admissions while a student there. Ricci, who testified before the grand jury but not at the probable cause hearing, died in January.

Sherman declined to characterize the expected effect of Coleman’s death on the prosecution case.

“I’ll let others make a judgment on this,” he said.