Terence Wheelock, 20, died in September 2005, three months after he was found unconscious in a cell in Store St garda station in Dublin city centre.
According to gardaí, Terence tried to hang himself.
To mark his 21st birthday yesterday, the Wheelock's protested outside the Dáil with the Maloney family, whose son John Junior collapsed and later died after being released from garda custody.
Both families claimed they have been denied justice and demanded the Government set up independent investigations into the two deaths.
Larry Wheelock, Terence's brother, insisted there were too many unanswered questions and a string of inconsistent accounts from state bodies.
"All we are looking for is answers into Terence's death and an independent public inquiry is the only way to get those," he said. "That is not too much to ask for in a civilised society.
"I'm sure Michael McDowell would expect the same if he was in a similar situation."
Petitions backing the two families were signed by dozens of relatives, friends and supporters and handed to Labour Party justice spokesman Joe Costello to present to the minister.
Teenager John Maloney Junior, from Crumlin in Dublin, was arrested in May 2003 and detained at Rathfarnham Garda Station. Less than an hour after his release he was found lying unconscious and died 11 days later in hospital.
An open verdict was returned at an inquest into the 18-year-old's death.
John's mother Sandra Maloney said: "They denied they ever had my son.
"I heard it on the radio that there was a lad found unconscious and I recognised that it was my son. My husband went to the garda station and they said he was in Tallaght Hospital with a bump on his head."
Ms Maloney said her son did not sign any release forms before leaving Rathfarnham Garda Station and he did not collect his ring and bracelet.
Ms Maloney also claimed Johnny's body was covered in bruises on his chest, hips, back and neck and that he had marks on his kneecaps.
"We just want the minister to listen. He has a son as young as my lad. His son comes home to him, my son doesn't come home to me. We just want the truth, that's all we want," she added.