John Brady was found dead in a cell at Strand Road police station
The family of a dissident republican found dead in a Londonderry police station have said they are concerned about how he died.
John Brady, 40, was taken into custody in Strand Road on Friday over an alleged assault. It is understood he took his own life on Saturday.
Mr Brady's sister, Lorna, said she wanted to know exactly what happened.
"I campaigned for justice for John when he was alive and I'm willing to campaign in his death, she said.
"Because until the day I die I want to find out the truth.
"Five weeks to go until he should have been released and this happens."
Mr Brady was jailed for killing a police officer during the Troubles, and released under the Good Friday Agreement. His licence was later revoked and he was returned to prison in November 2003.
He was on weekend leave when he was arrested.
His mother, Margaret, said that she was "devastated" at his death and said that her son was a lifelong republican who "knew the dangers he faced" but added that "his war was over".
"John should have been out in five weeks," she said.
"John's done 18 years inside and I've waited for this day, the day he would be released for good, but he'll never be released now.
"All they are releasing to me now is a body in a coffin."
A post mortem examination is to be carried out later on his body.
Police Ombudsman Al Hutchinson has launched an investigation.
Last year, Mr Brady was charged with attempted murder but this was dropped over concerns about DNA evidence.
He had been charged with putting a bomb under the car of a former RIR soldier in 2002.
However, the case was reviewed and dropped, based on a judge's criticism of low copy number DNA evidence during the Omagh bomb trial.
Mr Brady had been imprisoned for the murder of a police officer in 1989.
In 1991, he pleaded guilty to killing RUC Reserve Constable David Black who died after an under-car booby-trap bomb exploded near his home on the outskirts of Strabane.