Catholic police officer Michael Ferguson shot dead by the Provisional IRA in Derry in 1993
A 51 year old man had been arrested under Section 41 of the Terrorism Act 2000.
He had been taken to the Serious Crime Suite at Musgrave Police Station for questioning.
A PSNI spokesperson said: “The 51-year-old man arrested has now been released.
“The investigation continues.”
Two men – aged 64 and 51 – were arrested earlier this year for questioning but later released.
Michael was a 21 year old single man from Omagh.
The Senior Investigating Officer, Detective Inspector Conor Sweeney from Legacy Investigation Branch previously said: “Michael, along with two colleagues, were attending a call to the Richmond Centre in Derry at around 2pm.
“Michael remained on the street when his two colleagues entered the shopping centre.
“A lone gunman approached Michael from behind and shot him twice in the back of the head.
“The gunman made off on foot along Shipquay Street before entering Castle Street in the direction of the Bogside.
“We are following a number of definite lines of enquiry and I believe we are extremely close to progressing criminal justice action against Michael’s killers.
Sketch of the IRA gunman
“The gunman did not have his face covered and was wearing a distinctive green jacket. I believe that someone knows who this gunman was.
“Michael was a young man murdered while responding to a reported theft from a local shop. I would ask everyone listening to just stop and think about that for a second.
“Murdered for no other reason than he was providing a service to help local businesses, local community and local people.
“In the years since Michael’s murder, circumstances and allegiances may have changed, people’s lifestyles change and I want those who know who was involved that day to search their consciences and come forward to the police.
“I am aware that time has passed since the murder but it is not too late, if anyone now feels they are able to talk to us, we are ready to listen.
“To those involved I would appeal to them to do the right thing and make a difference to Michael’s family. They will no longer have to live with the worry that someday soon police are going to knock on their door.”
Detective Inspector Sweeney continued: “We are appealing for assistance from the local community who we still believe can help us, despite the amount of time which has elapsed.
Scene of the murder of Constable Michael Ferguson in Shipquay Street
“Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.”
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