Progressive Unionist Party member Billy Hutchinson has been released from police custody.
The former MLA was one of seven people being held by police investigating the murder of north Belfast schoolboy Thomas Devlin. Six others remain in custody.
Thomas, 15, was stabbed close to his home in August 2005.
No one has ever been charged with Thomas Devlin's murder.
Police believe his killers are from the Mount Vernon area, where Mr Hutchinson is a community worker.
Mr Hutchinson's arrest sparked a protest outside Antrim police station on Saturday.
PUP leader Dawn Purvis tonight welcomed the release of Billy Hutchinson but said questions still remained regarding the need and manner of his arrest.
Ms Purvis said, "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"?
"Allegations such as those made towards Billy Hutchinson could be extremely damaging. I am glad that he has been released without charge".