Who stole this money ?

A friend of my dad was putting 10,000 $ in a safe at his office at the Embassy in which he works in ................. He is a diplomat and he works at this embassy , in his office there is a safe, he put 10,000 $ of his money in that safe and locked it ........... All people at the embassy knew that he was putting this huge amount of money in his safe cos he talked about it ............ 2 days after he put the money in, All that money got stolen ......... My dad's friend is so sad and so surprised that how come money in a safe in an Embassy would get stolen and it's the money of a very big diplomat ........... My question is : The person who stole this money is it a person who works at the Embassy ? Why cant we say that someone jumped from outside without the guards seeing him and stole the money ? ......... MY dad 's friend says he is sure 100 $ that the one who stole this money is a person of those working at the embassy and not one from outside cos anyone from outside; from where will he bring the specific key to that safe ? ....... The safe was locked up with its keys when he put the money in so I am sure that the one who stole the money was a person working at the embassy as he has the key of that safe ........... What do you think ? How can my dad's friend prove who stole his money ?