MI6 sent the man to the village of Waziristan in Pakistan with a mission to go undercover in a base of the Taliban and al-Qaeda (terrorist group banned in Russia) fighters, according to the report. During the mission, the spy posed as a jihadi fighter and had to wash dismembered bodies of Taliban soldiers before burying them, while also witnessing an entire family accused of spying for the US being beheaded, the newspaper added.
After returning to the UK, the man was in "extreme stress," had violent outbursts and suffered flashbacks, news outlet reported. Eventually, he murdered his own child after some time since going back home, according to the leaked documents.
The report said that the individual got the highest score on an emotional instability test he had undergone before going on the mission and was still sent there. The man also told experts that he had been sexually abused as a child and had a criminal record, the newspaper added.
After the murder, the man was arrested and transferred to a secure psychiatric facility.
"He was an incredibly vulnerable man and his child was left in the most vulnerable of circumstances; circumstances which could have been safeguarded had more care been taken. He had served his purpose and was no longer the concern of his employers. He was used," a lawyer, who represented the former spy in court, told the media.
The trial was recently held in secret and the person's name and location have been kept anonymous, according to the newspaper.