SOFIA (Reuters) - A Palestinian who escaped from Israeli custody after being convicted of a 1986 murder has died at the Palestinian embassy in Sofia, Bulgarian prosecutors said on Friday.

Policemen stand outside the compound of the Palestinian embassy in Sofia, Bulgaria February 26, 2016. REUTERS/Stoyan Nenov

Police sealed off the mission building in the capital as an investigation began into the death of Omar el-Nayef, who was jailed along with two other men for killing Jewish ultra-orthodox seminary student, Eliahu Amedi, in Jerusalem.

Prosecutors said in an initial statement they had been alerted by a representative of the Palestinian mission in Bulgaria “about a man who died as a result of violence” but a spokeswoman for the prosecutors later said no signs of violence were found on his body.

She said Nayef was found in the mission’s back yard and prosecutors were investigating whether he was pushed or fell from a high floor, as well all other possible causes.

The mission, which is not guarded by Bulgarian security forces or its own guards and does not have camera surveillance, confirmed he was Omar el-Nayef.

“Omar (el-Nayef) Zayed is a martyr,” the Palestinian ambassador to Bulgaria, Ahmed Al-Mathbouh, told reporters. “We believe that those who persecuted him could have carried out something against him.”

Palestinian sources said he had been shot and a Palestinian prisoners’ association and the militant Popular Front for the Liberation of Palestine blamed Israel for his death, while President Mahmoud Abbas condemned what he called a “crime”.

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An Israeli Foreign Ministry spokesman said it had learned of his death in the media and was studying the information. Amedi’s sister, Yaffa Pinhasi, told Israel’s Channel 1 television that she believed Israeli agents were behind the killing.

“Whoever did this deserves praise,” she said.

Nayef was sentenced to life in prison for the murder but escaped in 1990 while being moved to hospital after he began a hunger strike. He first went to the Palestinian Territories before fleeing to an Arab country and then to Bulgaria, where he had lived since 1994.

Bulgarian authorities had sought to detain him following an extradition request by Israel in late December, prompting him to seek refuge at the Palestinian mission and leading to a country-wide search after Nayef could not be found at his Sofia address.

Official Palestinian news agency WAFA said Abbas had ordered an investigation into the circumstances of Nayef’s death.

“The president has condemned the crime in the strongest terms possible and has ordered the members of the (investigation) committee to travel immediately to Bulgaria to discover what happened,” WAFA said.

Abbas’s spokesman Nabil Abu Rdainah said the presidency would pursue the issue with Bulgarian authorities.

Bulgarian chief prosecutor Sotir Tsatsarov told reporters there was evidence Nayef had been living at the embassy. He also said Nayef had been alive when medics arrived at the embassy early on Friday but died shortly after.

Bulgarian Prime Minister Boiko Borisov, who returned from a visit to the Palestinian Territories and Israel late on Thursday, said Nayef’s extradition had been brought up in meetings by both the Palestinian and Israeli authorities.

“I told both sides that Bulgaria respects the rule of law and will follow the legal procedures in the case,” he told reporters in parliament on Friday.