Amman left prison just a matter of days ago after serving half of his more-than three year sentence, it is understood.
He was sentenced in December 2018 for possessing and distributing terrorist documents.
The then 18-year-old, who was described as 'knife-obsessed', was found with a stash of bomb-making and close-combat manuals - including one titled 'How to Make A Bomb in Your Kitchen'.
Amman, from Harrow, Middlesex, also shared Al-Qaeda propaganda on a family WhatsApp group, exposing relatives as young as 11 to violent material.
The North West London College student shared bomb making schematics via Skype and an entry of a seized notebook allegedly outlined his "goal" to die as a martyr, a court heard at the time.
In other online chats, Amman told his girlfriend of his hatred for “kuffars” (non-believers), his allegiance to ISIS and his wish to carry out a terror attack.
In one message he even encouraged his girlfriend to behead her own “kuffar parents”, the court previously heard.
"There was nothing that could be done to keep him behind bars under existing laws."