Six Canadian prisoners are suing authorities for C$15m ($8.6m) after witnessing the murder of a fellow inmate.

Prisoner Anthony George savagely assaulted and killed his cellmate Adam Kargus on 31 October 2013 as inmates of Elgin-Middlesex Detention Centre in London, Ontario, were locked up nearby.

Despite the incident being caught on CCTV, inmates were forced to shout and bang on their doors in a failed attempt to gain the attention of staff. Regulations state that all cells must be checked every hour, but this was not followed through.

The filing states that the men are now suffering from post-traumatic stress (PTSD) and other lasting symptoms of psychological trauma.

Prisoners were made to stay in the cell for up to two weeks following the assault and did not receive professional counselling from authorities. They also allege the killer bragged about the murder the next day, adding to their distress.

Anthony George, who was 32 of the time of the offence, was charged and sentenced to life in prison for second-degree murder in September. He will not be eligible for parole for at least ten years.

The men recounted the harrowing circumstances of Kargus's murder in the filing. They also allege staff did nothing when Kargus requested to be moved from his cell. One man watched the incident from his cell while the others listened nearby.

They "witnessed Adam's face at his cell window while George held him in a choke hold and made loud sounds like a 'war whoop.' [He] could see the terror in Adam's eyes as he was choked into unconsciousness and lowered to the floor. [He] could see George apparently stomping on Adam and committing other assaults for a prolonged period of time. He could see blood all over the windows of Adam's cell.

"Over a prolonged period of time, [they] heard repeated screams and other cries for help from Adam as well as various other sounds associated with a prolonged and vicious assault," the statements say.

"Several times during the brutal and prolonged assault (inmates) heard Adam scream in pain, yell for help, plead to be released from the cell and at one point cry out that he was being raped. (Inmates) also heard repeated loud banging of the cell door."

"I don't think that even those who have horrible experiences in their lives can match what happened that night," their lawyer Kevin Egan said.

"It was so gruesome and long-lasting and they were so helpless to do anything that no matter how hardened or how many other horrible experiences they might have gone through, this was by far the worst and most devastating to their psyche."

According to the London Free Press, the men have asked not to be named following acts of retribution by staff and other prisoners.

"I've been involved in organised crime. I've done all kinds of things for money. I don't know how I'm going to deal with this," one man said.