Omar Nayef Zayed, a Palestinian fugitive who had taken refuge at the Palestinian Authority's embassy in Sofia, has been found dead at the PA's embassy in the Bulgarian capital.
Palestinian Authority President Mahmoud Abbas ordered an investigation into what he called Zayed's assassination.
Zayed, 52, escaped from Israeli custody over 25 years ago after being convicted of murdering an Israeli yeshiva student in 1986.
Last month it was reported that Zayed had been given 72 hours to turn himself in for extradition to Israel or face arrest.
On Friday Bulgarian authorities were investigating the suspected murder, the Sofia News Agency reported.
The Bulgarian prosecutor’s office said Friday that an embassy official "had reported the death resulting from violence" in the embassy, the news agency reported.
Senior Palestinian officials and his family claimed Zayed was assassinated by Israel, Palestinian news outlet Ma'an reported.
Palestinian Deputy Minister of Foreign Affairs Taysir Jaradat told Ma'an that embassy staff found Zayed lying in the embassy's garden covered in blood. He was rushed to hospital but died en route.
Issa Qaraqe, the head of the Palestinian Committee for Prisoners' Affairs, accused Israel's Mossad of being behind the death.
Qaraqe told Ma'an that it was an act of "international piracy" and he demanded an international investigation into the death.
Israeli authorities made a formal request for Zayed's return on December 15, 2015.
Zayed has reportedly been living in Sofia since 1994 and has Bulgarian residency while his wife and three children all carry Bulgarian citizenship.
Two days after Israel demanded Zayed's return, Bulgarian authorities raided his home, arresting his 18-year-old son while Zayed was given succor at the PA embassy.
Zayed escaped prison in 1990 after eluding guards during a hospital visit, making his way to Bulgaria four years later where he was granted residency.
In a statement released last month by PA envoy to Bulgaria, Ahmad Madbough, said the embassy does not intend to comply with the extradition order and has yet to turn Zayed over to Bulgarian authorities.
On Thursday, Bulgarian Prime Minister Boiko Borisov met with Prime Minister Benjamin Netanyahu in Jerusalem and separately with Palestinian Authority President Mahmoud Abbas in Ramallah.