THE Scots army officer who commanded a shadowy British military intelligence unit in Northern Ireland which colluded with terrorists who murdered civilians during the Troubles should be questioned as part of a police probe, the families of victims have said.

Brigadier Gordon Kerr, who is originally from Aberdeen, ran the Force Research Unit (FRU) whose officers 'handled' top-level paramilitary informers. The FRU's most prized double-agent - Freddie Scappaticci, codenamed Stakeknife - who allegedly worked for military intelligence inside the IRA was arrested on Tuesday and questioned for four days about dozens of murders as part of Operation Kenova, an investigation into the activities of Stakeknife and collusion by the security forces.

The arrest of Scappaticci comes 15 years after the Sunday Herald first named him as Stakeknife in May 2003. The Sunday Herald also named Kerr as the head of the FRU in November 2000.

The probe, led by Chief Constable Jon Boutcher, from Bedfordshire Police, involves a team of 48 detectives who are interviewing current and former police officers in Northern Ireland, members of the British army and MI5 officers.

The whereabouts of Kerr, now 70, are currently unknown, and it is understood he is no longer in the armed forces. Bedfordshire Police would not confirm whether Kerr has been or will be brought in for questioning, but relatives of victims, who believe their loved ones were killed due to FRU operations, want Kerr probed. Last night, the SNP’s Northern Ireland spokeswoman insisted “no one is above the law”.

John Finucane, 37, was eight-years-old when two UDA gunmen burst into his home and shot his father fourteen times when he and his family were eating Sunday dinner. Pat Finucane, a prominent human rights lawyer who represented republicans, was killed in 1989 after alleged collusion between FRU officers and loyalist paramilitaries, including Brian Nelson, a former Black Watch soldier who became head of intelligence for the terror group the Ulster Defence Association.

John Finucane, a solicitor who stood as a Sinn Fein candidate, called for “greater scrutiny” of Kerr’s role at the time of his father’s death.

He said: “Given the unit Kerr ran has led to the deaths of so many people we have always found it strange that there hasn’t been any scrutiny of what Kerr was doing." Finucane added: "Gordon Kerr is very much at the centre of the actions of the FRU...Kerr’s role in all of this needs to be examined. We may not necessarily get justice, but we want the truth. Those who were in charge tend to be protected."

He said that if allegations were true that "Scappaticci was killing people at the behest of those in charge" then the question was not "who pulled the trigger, it’s who pulled the strings. It’s something that isn’t going away no matter how much the British government wants it to”.

When asked whether he has confidence in Operation Kenova, Finucane said: “I don’t have confidence in a process that doesn’t directly involve the families. A police investigation will only gather evidence and submit that to the prosecution. It is a fundamentally flawed process from the outset. I wouldn’t be optimistic that Kerr will be questioned or prosecuted.

“Allegations of collusion deserve a process where those directly affected have the ability to examine documentation and ask questions, and for people like Kerr to be represented too, because they may well say they were directed under orders by the [UK government] minister responsible at the time.”

Paul O’Connor, Director of the Pat Finucane Centre, a leading human rights group in Northern Ireland, added: “In respect of Kerr, we would be of the view that he and others in the chain of command, both within FRU and the wider security community, have questions to answer regarding their handling of agents such as Brian Nelson and the murder of Pat Finucane and others.”

Mark Thompson, founder member and CEO of Relatives for Justice, a group that supports families in Northern Ireland who were bereaved during the Troubles, also called for Kerr to be questioned by Kenova detectives.

He said: “Operation Kenova is a consequence of efforts by families to get to the truth about the so-called Dirty War. There are a number of questions that relatives have about that period and a strongly held belief that people were sacrificed to help protect other people."

Thompson said families were "hopeful" that Chief Constable Jon Boutcher "will get to the bottom of this. He’s built a trust and confidence with families that’s unprecedented. I have no doubt Jon Boutcher will arrest handlers and in my view, he needs to go where the evidence leads him. He needs to follow that evidence trail to the top. We would certainly say the Kenova inquiry would have to detain and question Gordon Kerr, if Jon Boutcher wants to retain his credibility.

“There is a murky backdrop to this that is isn’t just black and white. It’s not just about the people who pulled triggers. It’s about the nature of the system. Effectively the state was deciding who would live and who would die.

“The problem Jon Boutcher will have is if somebody like Gordon Kerr ends up in the dock we will have the domino effect which will go up the chain of command to the very highest level, and it will arrive at senior levels in Whitehall and Downing Street. From a reputational point of view, [as far as senior figures in Whitehall and Downing Street are concerned] that has tkaro be avoided at all cost.”

The SNP’s Northern Ireland spokeswoman, Deidre Brock MP, said Operation Kenova is staffed by experienced detectives who should be trusted to do their job.

She added: “Anyone who may have pertinent information should be questioned and should be willing to cooperate - and anyone who may have committed a crime should be reported to the appropriate prosecutor. No-one should be seen as being above the law and I trust the investigating team to do their job properly.”

A spokesman for Bedfordshire Police said: “I’m afraid we aren’t releasing any information regarding the individuals we are in contact with, or those who might be of interest. This week’s arrest was the first by Operation Kenova – we aren’t confirming the identity of the arrested man.”

Chief Constable Jon Boutcher confirmed on Friday that a 72-year-old man – who is believed to be Scappaticci – was bailed on Friday and will “return to police custody at a date in the near future”.

Boutcher said: “This arrest was a significant step in what continues to be an incredibly complex and wide-ranging investigation. My team is continuing to speak with witnesses and victims’ families and we are exploring a huge number of lines of enquiry.”

A Ministry of Defence spokesman said: “We are assisting the police in their investigation. As the investigation is ongoing it would be inappropriate to comment further.”