He had a ringside seat for the entire, bloody rise of ISIS, and by his own count killed dozens of innocent men, women and children. Now facing likely execution, Thahir Sahab Jamel disavows the black-clad Islamist army, but his Kurdish jailers say they’ve heard it all before.

In a jailhouse interview with FoxNews.com in the Kurdish-held city of Kirkuk, Jamel, 27, detailed how he joined Islamic State in 2013, served as a foot soldier in the takeover of Mosul a year later and, he claims, eventually became disillusioned with the dark vision of his fellow fighters.

“At the beginning, ISIS told us we would all go to heaven,” Jamel said, speaking under the watchful eyes of Kirkuk police guards. “But now that I am in prison it means I am going to the fire. I am going to hell.”

Handcuffed and partially masked, Jamel, who has been in solitary confinement since his arrest two and a half months ago, said he joined the terror group like many other young Sunni Muslim men opposed to the Shia-led government in Baghdad.

“A man named Salam talked to me and got me connected to ISIS. He told me I needed to be a jihadist and fight the Shia government. He convinced me to fight the government,” Jamel said. “I started getting involved as they were planning operations to begin in Iraq and Syria.”

Jamel lived with his mother and three brothers in Hawija, a smaller town just south of the oil-rich Iraqi city of Kirkuk. He had a decent, agriculture-related job, and his family did not understand why he wanted to throw in with the insurgents who would soon become the world’s most-feared terrorist army.

In the early days, Jamel said, most of the recruits were young men in their early 20s. But soon their ranks were swollen by experienced soldiers as old as 50 from Saddam Hussein’s old army. The battle-hardened men, also Sunni Muslims alienated by the Shia government, were experienced with small arms and heavy equipment.

The mission was to take over the nation, and kill infidels and fellow Muslims who stood in their way, he said.