Police ombudsman Al Hutchinson is to investigate Mr Brady's death
The police ombudsman has launched an investigation after a man died suddenly at a police station in Londonderry.
John Brady, 40, a well-known dissident republican, had been arrested on Friday night and was being questioned about an alleged assault.
He was held overnight. Police officers discovered his body at Strand Road police station on Saturday evening.
It's understood he took his own life. MP for West Tyrone Pat Doherty said the death needed to be thoroughly examined.
The police ombudsman, Al Hutchinson, said it was "too early" to determine the cause of Mr Brady's death and that a post-mortem examination would take place on Monday.
"Our office needs to conduct a fair, independent and impartial investigation into the death and we are dealing with the families," he added.
"It is important at this time of grief that Mr Brady's family have our sympathies and certainly have our assurance that we will conduct a fair and impartial investigation into the cause of his death."
Last year, Mr Brady was charged with attempted murder but this was dropped over concerns about DNA evidence.
He had been charged with leaving 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 device exploded near his home on the outskirts of Strabane.
John Brady was among those released after the Good Friday Agreement
He was initially released on licence in 1998 after the Good Friday Agreement, but his licence was later revoked and he was returned to prison in November 2003.
Mr Doherty, from Sinn Fein, said this was "a tragic loss" for the Brady family.
"There are obviously serious issues of concern about how John Brady died during daylight hours while in police custody," he said.
"While the full details surrounding this death are unclear it is vital that there is a full and open investigation by the Police Ombudsman."
The investigation into Mr Brady's death comes days after four staff at Maghaberry prison were suspended after a prisoner died in August.
John Anthony Deery, 50, a convicted sex offender, was found in his cell and died later in the Royal Victoria Hospital in Belfast.
The Prisoner Ombudsman Pauline McCabe is investigating that death.