Images of passengers and crew posing for selfies with EgyptAir hijacker Seif el-Din Mustafa have gone viral, but behind the smiles there was terror, confusion, a mentally unstable former criminal and a hint of darker political motives. Mustafa – accused of neglecting his children, drug abuse, and violence – is far from the incompetent geek portrayed in much of the media, said the co-pilot of the plane which was forced to fly to Cyprus.

In an exclusive interview with Newsweek, co-pilot Hamad el Kaddah – who was filmed escaping from the cockpit before dropping to the tarmac – has revealed the fear and confusion caused when Mustafa emerged from a toilet claiming to have an explosive belt. He also claimed that reports Mustafa simply wished to see his ex-wife, who is now living in Cyprus, don't tell the whole truth.

"He had a letter, he wanted to give it to the authorities over there. He wanted a translator and a lady and this lady is his ex-wife or something," Kaddah told Newsweek by phone as he returned to Cairo to speak to the authorities. "And he wanted to negotiate with the European Union, something about politics that I can't really mention."

Mustafa has become something of a joke figure since it emerged that his suicide belt was a fake and images of his selfie with Ben Innes from Leeds circulated. However Kaddah says it was no laughing matter when the 59-year-old Egyptian threatened to blow up the plane, leaving some of the stewardesses were in tears.

In a message relayed to the cockpit, Mustafa allegedly said: "Captain, the plane is hijacked. Go now to Cyprus, Turkey or Athens. If you land in any of the Egyptian land airports, it will be only one press on the button, everything will go, everyone will die. It's your decision."

It has also been revealed that Mustafa has been in prison on a number of occasions in Cyprus, Syria and elsewhere and bragged about killing three Israel soldiers.

Mustafa was described by an Egyptian foreign ministry official as "not a terrorist," but "an idiot." His former wife, Marina Paraschou, said he was indifferent to his daughter's death after she was killed in a car accident. In an interview with Phileleftheros daily she said: "This man never cared for his children for one minute, either when he lived here or when he went away. He only offered pain, misery and terror. And even now when he's in police custody, my children and I are afraid."

Paraschou said she had had no contact with her ex-husband for years except when she rang to tell him one of the four children they had together was dead. Mustafa reportedly replied: "And what do I care? I don't mind that she died."