TRENTON, N.J. - A New York man pleaded guilty Thursday to what experts said was the first ever proven case of black-market organ trafficking in the United States.

Levy Izhak Rosenbaum admitted in federal court in Trenton that he had brokered three illegal kidney transplants from people in Israel for U.S.-based customers in exchange for payments of $120,000 or more. He also pleaded guilty to one count of conspiracy to broker an illegal kidney sale.

His attorneys said Rosenbaum had performed a lifesaving service for desperately ill people who had been languishing on official transplant waiting lists.

"The transplants were successful and the donors and recipients are now leading full and healthy lives," Ronald Kleinberg and Richard Finkel said in a statement.

The lawyers added that Rosenbaum had never solicited clients, but that recipients had sought him out, and that the kidney donors he arranged were fully aware of what they were doing. They said the money involved was for expenses associated with the procedures, which they say were performed in prestigious American hospitals by experienced surgeons and transplant experts. The lawyers did not name the hospitals involved, nor are they named in court documents.

Prosecutors said Rosenbaum was fully aware he was running an illicit and profitable operation -- buying organs from vulnerable people in Israel for $10,000 and selling them to desperate, wealthy U.S. patients.

"A black market in human organs is not only a grave threat to public health, it reserves lifesaving treatment for those who can best afford it at the expense of those who cannot," said New Jersey's U.S. Attorney, Paul Fishman. "We will not tolerate such an affront to human dignity."

Each of the four counts carries a maximum five-year prison sentence plus a fine of up to $250,000. Rosenbaum also agreed to forfeit $420,000 in real or personal property that was derived from the illegal kidney sales.

The 60-year-old Rosenbaum is a member of the Orthodox Jewish community in New York, where he told neighbours he was in the construction business.

He was arrested in 2009 in a sweeping federal case that became the largest corruption sting in New Jersey history. He was one of more than 40 people arrested, including politicians and rabbis in New Jersey and New York. He was not a rabbi himself, but the image of rabbis illegally selling kidneys made international headlines.

Rosenbaum was arrested after he tried to set up a kidney sale to a man posing as a crooked businessman but who actually was government informant Solomon Dwek, a disgraced real estate speculator facing prison time for a $50 million bank fraud.

Dwek brought Rosenbaum an undercover FBI agent posing as his secretary, who claimed to be searching for a kidney for a sick uncle on dialysis who was on a transplant list at a Pennsylvania hospital.

"I am what you call a matchmaker," Rosenbaum said in a secretly recorded conversation. "I bring a guy (who) I believe, he's suitable for your uncle."

Asked how many organs he had brokered, he said: "Quite a lot," the most recent two weeks earlier.

For someone who was not a surgeon, Rosenbaum seemed in his recorded conversations to have a thorough knowledge of the details of kidney donations, including how to fool hospitals into believing the donor was acting solely out of compassion for a friend or loved one.

He was recorded saying that money had to be spread around liberally, to Israeli doctors, visa preparers and those who cared for the organ donors in this country. "One of the reasons it's so expensive is because you have to shmear (pay others) all the time," he was quoted as saying.

"So far, I've never had a failure," he said on tape. "I'm doing this a long time."

At a 2008 meeting with the undercover agent, Rosenbaum claimed he had an associate who worked for an insurance company in New York who could take the recipient's blood samples, store them on dry ice and send them to Israel, where they would be tested to see if they matched the prospective donor, authorities said. Donors would be brought from Israel and undergo surgery to remove the kidney in a U.S. hospital, according to court documents.

Critics and experts on organ trafficking say many U.S. hospitals do not have vigorous enough procedures for looking into the source of the organs they transplant because such operations are lucrative.

U.S. transplant centres are mostly free to write their own rules for screening donors. The questions they ask vary widely. Some hospitals require long waiting periods; others don't.

Under U.S. law, it is illegal for anyone to knowingly buy or sell organs for transplant. The practice is illegal just about everywhere else in the world.

But demand for kidneys far outstrips the supply, with 4,540 people dying in the U.S. last year while waiting for a kidney, according to the United Network for Organ Sharing. As a result, there is a thriving black market for kidneys around the world.

Art Caplan, a co-chairman of a United Nations task force on organ trafficking, said kidneys are the most common of all trafficked organs because they can be harvested from live donors, unlike other organs. He said Rosenbaum had pleaded guilty to one of the "most heinous crimes against another human being."

"Internationally, about one quarter of all kidneys appear to be trafficked," Caplan said. "But until this case, it had not been a crime recognized as reaching the United States."