Harendra Singh was back on the stand for a fourth day Thursday and detailed his relationship with former Town of Oyster Bay Supervisor John Venditto, as well as more revelations about former Nassau County Executive Ed Mangano.

Singh is the prosecution's star witness in the federal corruption trial for Venditto, Mangano and his wife Linda.

Singh testified that in 2013, Mangano handed him $3,600 in cash and asked him to swap it out with new bills. Singh said Mangano was afraid the money was marked after receiving it from a home contractor who had done work for the county executive and then kicked his fees back – hoping to curry favor with him.

Rather than question Mangano, Singh said he did as he was told even though he knew it was against the law.

"This was not something to be shared with anybody. This was not something legal. This was under-the-table money given to Ed Mangano for the work that was done at his house," said Singh.

Singh also testified that he spent thousands on limousine rides and car service for Venditto, his family and the men he describes as the supervisor's two lieutenants – campaign chairman Rich Porcelli and Deputy Town Supervisor Leonard Genova.

For Venditto, Singh said he paid for trips to Manhattan, with destinations like the Metropolitan Opera House and The Pierre hotel.

MORE: Prosecutor: Mangano, Venditto ‘earned their keep’ for bribes, kickbacks

Singh said in 2010, he paid more than $1,000 in vehicles for a bachelor party for Venditto’s son, Michael. He said he also spent more than $1,300 for Michael's fiancé’s bachelorette party transportation and more than $1,700 for vehicles on the couple's wedding day.

Singh said he wasn't even invited to the wedding. Michael Venditto went on to become a county legislator and state senator.

Singh also described how he allowed Venditto to use space in the basement at his restaurant, Singleton's, whenever he wanted. He described one instance in which Venditto was smoking in a basement banquet room. A potential customer saw Venditto smoking and became offended. Instead of kicking the town supervisor out, Singh said he built a more private conference room and allowed Venditto, and later Mangano, to use it at will.

When asked why Singh provided these services, he said his businesses were reliant on good relations with the county and the town.

"You don't question someone who, with one action, can throw you out from your investment," said Singh.

Singh testified earlier this week that he was able to secure a loan guarantee of $20 million by the Town of Oyster Bay through bribes involving both Mangano, Venditto and a no-show job provided to Linda Mangano.