Before he joined with militant Islamists, Mr. Storm, now 43, was an armed robber and, at 21, a prospective member of a criminal biker gang. In 1997, in his early 20s, he converted to Islam and moved first to Britain, and then to Yemen to learn Arabic. There, he befriended senior members of Al Qaeda in the Arabian Peninsula.
In 2006, according to his account, he lost faith in jihadism and turned on his terrorist comrades to become an informer for the Danish intelligence service, as well as for agencies in Britain and the United States.
Mr. Storm claims that information he provided helped lead to the drone killing of the American cleric and Qaeda recruiter Anwar al-Awlaki in Yemen in 2011 and also to the arrest that year of Ahmed Abdulkadir Warsame, a Somali aiding Al Shabab, a terrorist group in Somalia, and Al Qaeda in Yemen. His claims have never been publicly confirmed by the C.I.A.
In 2012, Mr. Storm broke with PET and started speaking to the news media.
He said he had worked directly with American and Danish agents and received monthly payments, but never rewards or help to restart his life — a source of great resentment to him.
Mr. Storm is apparently now hiding in a village in Denmark, saying he is fearful of his former comrades in the jihadist network who have threatened him online. In 2018, four people were convicted of threatening him on a Danish beach during a trip with his three children.
It was the strains of a dangerous double life, Mr. Storm said, that led to his PTSD. Today, he says, simple grocery shopping in the Danish countryside causes him fear.
“At night, I scream and kick,” he said in a telephone interview. “Just talking about it now makes me uneasy.”