One of the companies charged this week with manslaughter in the April death of laborer Carlos Moncayo at a New York City construction site is owned by a businessman who was once a central figure in a celebrated Suffolk County political corruption trial.

Sky Materials Corp., also accused of criminally negligent homicide and reckless endangerment over a trench collapse that killed the 22-year-old, is owned by Michael Cholowsky, a key witness in the 1999 trial of Suffolk Republican chairman John Powell.

Cholowsky, who ran trucking and sand mining businesses, became a government cooperator, and testified in federal court that he had paid $20,000 in bribes to Powell for access to the Brookhaven landfill.

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According to Newsday coverage at the time, Cholowsky helped federal agents make audio and video recordings, and at trial admitted lying on 4 years of tax returns and paying workers $100,000 off the books, as well as engaging in the bribe scheme.

Powell was convicted of conspiracy and extortion. Following the trial, Cholowsky received a year's probation for conspiracy to defraud the government after prosecutors wrote a letter vouching for his assistance.

On Wednesday, the Manhattan district attorney's office said Moncayo, who worked for Sky, died on April 6 when a 13-foot-deep trench collapsed, burying him in thousands of pounds of dirt at a site on Ninth Avenue being readied for a Restoration Hardware store.

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General contractor Harco Construction LLC and its site supervisor, as well as excavation subcontractor Sky Materials and its foreman were accused of maintaining unsafe conditions by failing to shore-up the trench and ignoring safety warnings from a site inspector for weeks.

Moncayo, an Ecuadorean immigrant who had taken an OSHA scaffolding course to qualify for working at the site, was undocumented, as were many other workers, said Manhattan District Attorney Cyrus Vance.

Sky, Harco and the two workers pleaded not guilty in the case. Sky attorney Brian Gardner, in a statement, said, "We are saddened by the accident, but it should not be the subject of a criminal prosecution."

Gardner said Sky didn't know if Moncayo and other workers were undocumented and in any event had no "policy to hire undocumented workers." Cholowsky's past involvement in Suffolk corruption and the Powell trial, he said, had no connection to the new case.

"We continue to be saddened by the loss of one of our employees," Gardner said. "You are asking about a matter that occurred over 15 years ago and is completely unrelated and irrelevant to the recent tragic accident."

Vance's office and the city's Department of Investigation both declined to comment on Cholowsky's past.

Sky, with facilities in Queens and Calverton, itself played a central role at the 1999 corruption trial. In a video later cited by jurors, Powell urged Cholowsky to keep a low profile, and told him to not label trucks, jackets and sweatshirts with "Sky Materials."

"Why are we putting our name on everything all of a sudden?" he complained.