Police said that their investigation has revealed that the blast that killed Ambassador Jamal al-Jamal on Jan. 1 did not occur inside the safe and no explosive device was part of the safe.
The cause of the explosion remains unclear.
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Police spokeswoman Andrea Zoulova told The Association Press that "mishandling remains the most likely option."
"There's a question whether he knew what he was dealing with," she added.
Police said in a statement that they need several more weeks to complete their investigation.
Police say they discovered 12 illegal weapons and explosives at the embassy dating from the 1970s and 1980s. Palestinian authorities have said the weapons were gifts from officials in Czechoslovakia during the Cold War.
The ambassador's death is being investigated as a case of negligence.