"We still think this is a civil matter, not a criminal matter," Mr. O'Brien said outside court.

Mr. Gerulaitis, 40, a retired tennis star who was accustomed to a life of fame, wealth and glamour, died in September in the most mundane manner, napping in the pool cottage of a Southampton estate owned by a real estate executive, Martin Raynes.

After a seven-month investigation, the authorities concluded that the improper installation of the pool heater in the basement of the cottage caused the athlete's death.

The heater, manufactured by Teledyne Lars, was intended to be installed outdoors. For indoor installation, a ventilation kit was provided, but it was not used, investigators said. They said that a representative of Teledyne Lars had inspected the installation days before Mr. Gerulaitis died, at the request of Recreational Concepts, after a complaint by Mr. Raynes that the pool was not heating properly. The representative warned the company that the heater was not properly ventilated, but no changes were made, the authorities said.

Investigators said the pool heater was installed in April 1994 with a plastic exhaust pipe extending from the heater and hanging on a cord from the basement ceiling. The open end of the pipe faced the slats of a louvered door -- too short to reach the outside of the cottage.

With a $1.44 pipe extension, Mr. Catterson said, the fumes would have been dispersed safely away from the cottage. Instead, he said, the carbon monoxide was drawn by an air conditioner through a forced-air heating vent into the cottage where Mr. Gerulaitis was sleeping. When he died, the carbon monoxide level had reached 2,700 parts per million, Mr. Catterson said.

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"Death could come in 20 minutes at that level," Mr. Catterson said. "It's silent, it's odorless, it's tasteless." He had no explanation for why no previous problem occurred between the April installation and Mr. Gerulaitis's death in September.

During the arraignment, the assistant district attorney, Linda Spahr, said that Mr. Torpey had an installation manual for the heater, which indicated that it should be installed outdoors or equipped with the ventilation kit.

Mr. Torpey, who grew up in Suffolk County and moved to Sag Harbor four years ago, had worked as a pool mechanic for more than 12 years, Mr. O'Brien, his lawyer, said. He said his client was surprised by the criminal investigation, although he knew that an insurance company had been looking at the case.

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Legal experts said that the prosecution of the company and the mechanic was unusual, and that it might be difficult for the government to prove criminal liability. Criminal negligence is an offense that involves the failure to "perceive that a substantial and unjustified risk" could cause a homicide to occur.

"This could make legal history because in most civil-criminal borderline situations, the wrongdoer relies on insurance to bail him out of a mistake," said Samuel E. Rieff, a Garden City lawyer and a former Nassau County prosecutor. "And wouldn't it increase the care people take when working with hazardous materials if they knew they stood to be punished personally?"

Other lawyers questioned whether the case amounted to a form of celebrity justice.

"If the person who died had been someone with less standing in the community, less famous, then I don't even know whether a grand jury would have even heard this case," said Andrew Siben, a lawyer whose firm specializes in negligence cases.

Robert C. Gottlieb, a criminal defense lawyer in Commack who ran against Mr. Catterson in 1992, said that high-profile cases involving celebrities create pressure to act.

"Usually matters like these are taken care of in civil court," Mr. Gottlieb said, "and to elevate this to criminal court is not only unusual, but very difficult."