Three people were arrested last week on suspicion of organ trafficking, one of whom is a doctor already standing trial for similar offenses in the past.

The three were arrested on Tuesday at the end of a month-long undercover investigation. On Wednesday, the Rishon Letzion Magistrate’s Court ordered Dr. Michael Ziss and Shlomi Biton held without bail, and released the third suspect to house arrest.

Ziss, a surgeon, was extradited from Ukraine to Israel in 2009 on similar suspicions. He and Biton were eventually charged with organ trafficking and conspiracy to commit a crime in that case, which is still being heard by the Be’er Sheva District Court. But in October 2014, the court rejected the prosecution’s request to keep Ziss in jail until the end of his trial.

In the new case, the three men are suspected of running a complete trafficking operation: locating people willing to sell a kidney, locating patients willing and able to pay for one and then arranging the transplant. Police said the traffickers would approach poor people who were in debt and propose that they sell a kidney for transplant. The actual transplants were performed in a Turkish hospital, with the donors posing as relatives of the patient. The patients paid hundreds of thousands of shekels for the service.

At Wednesday’s court hearing, police said the ring was working on dozens of such deals. In at least one case, the transplant was actually completed, and there is evidence that the patient paid Ziss. The other cases were at earlier stages of the process.

The National Transplant Center stressed that it was not involved in any of the transactions and that no illegal transplants were performed in Israel.

Selling organs is illegal everywhere in the world except Iran. But Israel is considered a major player in the organ trafficking business, and the number of Israelis who have sold kidneys via traffickers is estimated at between 10,000 and 20,000.

Although recipients pay hundreds of thousands of shekels for the kidney, the donor, according to various reports, gets only between 60,000 and 100,000 shekels ($16,000-$26,000). The rest of the fee goes to the head of the trafficking ring, the doctor overseeing the transplant, the lawyer who prepares the false affidavits, and expenses such as hospital and hotel fees.

One reason Israel is considered fertile ground for organ traffickers is that postmortem organ donation rates are among the lowest in the Western world, mainly for religious reasons. As of January 2016, 1,153 Israelis were awaiting organ donations, including 843 who needed kidneys.