Coroner Thomas Noguchi said today that his office will make "detailed studies" on the purity of cocaine and heroin blamed for the respiratory failure that killed John Belushi.

Noguchi said mixing the illegal drugs, in a process users call "speedballing," can often be fatal.

"The drugs paralyze the brain function. The entire system fails--there is a complete disruption of the central nervous control," Noguchi said. "The heart stops, and breathing becomes irregular. Unless the brain is functioning and well coordinated, the human body cannot continue."

The coroner also said that Belushi's weight and reportedly poor physical condition had "nothing to do with" his death.

"If he had been in the best of health, he would have died," said Noguchi. "The combination of the cocaine and heroin would have killed anybody."

Belushi, 33, was buried Tuesday on Martha's Vineyard off Cape Cod.

Noguchi reported Wednesday that Belushi had injected a combination of cocaine and heroin before his death last Friday, and that the drugs apparently triggered respiratory failure.

Both drugs were discovered in Belushi's Chateau Marmont bungalow, where he was found dead, as well as in his body, Noguchi said.

Belushi's Beverly Hills physician said the actor was allergic to such drugs as cocaine and said he had warned Belushi that cocaine use could trigger a reaction leading to repiratory failure.

Police Chief Daryl Gates said officers could not immediately say whether Belushi injected the drugs himself or had help. But he said investigators believed the drugs were "something he wanted."

Gates said that his department "will follow up as much as we can" the question of who supplied the drugs, but that it probably could not be determined whether the woman with Belushi before he died--rock singer Cathy Evelyn Smith--forced any drugs on him.

Belushi's widow, Judith Jacklin, told the Chicago Sun-Times she was "interested in the girl, and what her story is." Jacklin's in-laws and her family "want to find out more about this person."

The woman, Jacklin said, had been thrown out of Belushi's room a few nights before Belushi died, by Bill Wallace, a martial arts expert who traveled with Belushi.

"Two days before he died John told Bill to throw her out of the room. Somehow she showed up and got in. I wish I knew more."

Jacklin also said actor Robert De Niro and comic Robin Williams had been with her husband until about 3 or 4 a.m. last Friday. His body was found in his hotel room shortly after noon. The guests left while Belushi was sleeping, but thought he was all right, she said. De Niro's business manager, Jay Julien, said today that the actor was currently in New York but that he did not know whether he had been in Los Angeles last Friday.