PRAGUE - The Palestinian ambassador to Prague who died in a blast in January was most likely killed by a decades-old charge of Semtex plastic explosive concealed in a book, a newspaper reported on Tuesday citing a police investigator.Police had decided Jamal al-Jamal was not assassinated, but had simply unwittingly opening a book booby-trapped years earlier, the source told daily newspaper Mlada Fronta Dnes. "It was an unfortunate accident. The ambassador was a thorough man who wanted to put some old things in order, and among them there were two books with explosives," the paper quoted the source as saying.It did not explain why such a book might have been left at the embassy in Prague.But past statements by police had suggested al-Jamal may have been killed by a device used to secure an old safe.Officers investigating the explosion found other explosives and firearms at the mission dating back to the Cold War.The Palestinians had said they were old gifts from officials of Communist Czechoslovakia, which has friendly relations with the Palestine Liberation Organization of the late Yasser Arafat.A police spokeswoman said on Tuesday she could not comment on the investigation. The embassy spokesman was not immediately available for comment.The explosion took place as the Palestinian mission was moving its embassy and residence in the capital. Al-Jamal died of his wounds in hospital."We are awaiting another expert opinion, but it was Semtex with 99.9 percent probability. The explosive was roughly from the 1970s. It was at least 30 years old," the police source told the newspaper.Semtex, which was used to blow up Pan Am Flight 103 over the Scottish town of Lockerbie in 1988, has been produced by Czech company Explosia since the 1960s. Large amounts of the explosive were shipped abroad during the Cold War.