Senior Progressive Unionist Party member Billy Hutchinson, a former assembly member, has been released from police custody pending a report.
He was one of seven people held by police investigating the murder of north Belfast schoolboy Thomas Devlin.
Another male has been similarly released. Five other people remain in custody.
Thomas, 15, was stabbed close to his home in August 2005. Police believe his killers are from the Mount Vernon area.
The one-time MLA's arrest sparked a protest outside Antrim police station.
PUP leader Dawn Purvis said that questions remained unanswered regarding Mr Hutchinson's arrest.
"I would like some answers as to why the police felt the need to arrest him at all and why that information was leaked to the media?" she said.
"Allegations such as those made towards Billy Hutchinson could be extremely damaging. I am glad that he has been released without charge".
No-one has ever been charged with Thomas Devlin's murder.
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