PRISTINA, Kosovo – European Union police in Kosovo on Wednesday asked for “hard facts” to back up claims made by an investigator that civilian detainees of the Kosovo Liberation Army were shot to death to sell their kidneys on the black market.

Council of Europe investigator Dick Marty rocked Kosovo with his report, released Tuesday, that also suggested that Prime Minister Hashim Thaci was once the “boss” of a criminal underworld behind the alleged grisly trade.

Thaci was the rebel Kosovo Liberation Army’s political head during the 1998-99 war for independence from Serbia. His party just won Kosovo’s first general elections since it declared its independence from Serbia in 2008.

An earlier EU investigation into claims that organ harvesting took place in northern Albania did not come up with any proof, EU police mission spokeswoman Karin Limdal said.

“The prosecution bases their investigation and the indictments on hard facts and proofs,” Limdal said.

“If there is any evidence to any of those allegations put forward in this report the people that sit on that evidence should bring them forward,” she said.

Marty, a Swiss senator, led a team of investigators to Kosovo and Albania in 2009, following allegations of organ trafficking by the KLA published in a book by former U.N. War Crimes tribunal prosecutor Carla Del Ponte who said she was given information by Western journalists.

Marty’s investigation found that there were a number of detention facilities in Albania, where both Kosovan opponents of the KLA and Serbs were allegedly held once the hostilities in Kosovo were over in 1999, including a “state-of-the-art reception center for the organized crime of organ trafficking.”