James Bulger's mother is considering legal action to halt the release of her son's killers following claims that one of them tried to strangle a fellow inmate.
Robert Thompson allegedly attacked a 15-year-old boy at his secure unit by wrapping an electrical flex around his neck, according to the Sunday People newspaper.
Announcing last year that Thompson and Jon Venables were eligible for parole, the Lord Chief Justice, Lord Woolf, said "neither has shown any aggression of propensity for violence during his period of detention".
James' mother, Denise Fergus, said she wanted to know if staff at the unit had covered up the incident, alleged to have occurred in March 1999.
"It is outrageous they should have kept this a secret," she said.
"The Lord Chief Justice was wrong to parole Thompson and Venables so soon."
She added: "I will be consulting my lawyer to see if we can take this back to the High Court to get the parole decision changed".
The alleged victim of the attack was reportedly planning legal action against Thompson but Thompson's solicitor, Dominic Lloyd, said that the allegation was untrue.
Meanwhile The Express claimed to have details of Thompson attacking another teenager at the secure unit in January 1997. The newspaper says the Home Office was notified of the incident but no details have been made public until now.
Thompson and Venables, now 18, were 10 when they beat two-year-old James to death on a railway line in Liverpool in February 1993. They may be released later this year and a recent High Court ruling granted an open-ended injunction protecting their anonymity when they are freed.