Michael McConville called for an independent investigation into his mother's death

Sinn Fein Leader Gerry Adams at an election rally at the Devenish Complex, Belfast.

Police Service of Northern Ireland Chief Constable Matt Baggott said the decision to free Mr Adams taken by an independent judge

Northern Ireland's chief constable has said criticism of his force's arrest of Gerry Adams was unfair and inappropriate.

The Sinn Fein president was questioned for four days at Antrim police station by detectives investigating the 1972 murder of Belfast mother-of-ten Jean McConville.

Police Service of Northern Ireland (PSNI) chief Matt Baggott said it would have been wrong to treat Mr Adams any differently from anybody else.

Sinn Fein has claimed there is a "dark side" opposed to the peace process within the police force and blamed an embittered rump left over from far-reaching reforms for their leader's detention.

Mr Baggott said: "Questioning the motivation or impartiality of police officers tasked with investigating serious crime in this very public, generalised and vague manner is both unfair and inappropriate.

"The arrest and questioning of Mr Adams was legitimate and lawful and an independent judge subsequently decided that there were grounds for further detention."

His remarks came as Stormont First Minister Peter Robinson said his Democratic Unionist Party (DUP) had been on the verge of putting a motion before the power-sharing Assembly calling for Sinn Fein's exclusion from the ruling Executive.

It was considered following comments made by senior republicans - including Deputy First Minister Martin McGuinness - that they might review their support for the police if their leader was charged.

Mr Robinson said he stopped short of the move when Sinn Fein "corrected" its position - a reference to Mr Adams' statement of support for the Police Service of Northern Ireland (PSNI) upon his release from custody on Sunday.

Mr Baggott refuted any suggestion that there was a dark side to policing.

He said under reforms to the police force which faced paramilitaries during Northern Ireland's 30-year conflict, the Royal Ulster Constabulary (RUC), there were numerous ways in which policing concerns could be addressed.

They include the Human Rights Commission, the Policing Board made up of political and independent members and an ombudsman who investigates complaints.

Mr Baggott added that decisions on whether or not to prosecute were made independently by the Public Prosecution Service (PPS).

"In a democracy, the police are tasked with following the evidence without fear or favour and in accordance with the law.

"The PSNI are committed to doing so regardless of any undue pressures. It would have been wrong to treat Mr Adams any differently to other citizens."

The director of an oral history project on the Northern Ireland Troubles - part of which was relied upon by police to question Mr Adams about a notorious IRA murder - has rejected any suggestion that it was set up to "get" the Sinn Fein president.

New York-based Irish journalist Ed Moloney insisted Mr Adams's vocal criticism of the Boston College-backed endeavour was based on "almost complete ignorance", as he had not seen the contents of the archive.

He said: "In the past few days a concerted attack has been made on the integrity of the Belfast Oral History Project, led by the leadership of Sinn Fein, in which the claim has been made that this was a 'Get Gerry Adams' enterprise designed to embarrass and discomfort Mr Adams.

"I wish to refute this allegation in the strongest possible terms."

The Belfast Project at Boston College involved interviewing more than 25 former paramilitaries on their recollections of the Troubles on the understanding their accounts would not be made public until after their deaths.

But that assurance was undermined when a US judge ordered that audio tapes that referred to the murder of Mrs McConville be handed over to detectives from the PSNI.

After four days of questioning at Antrim police station, Mr Adams claimed most of the evidence detectives presented to him about Mrs McConville's death was based on allegations levelled by project interviewees, two of whom were now-dead former IRA members Brendan Hughes and Dolours Price.

Prosecutors in Northern Ireland have been asked to assess a police file on Mr Adams to decide if any charges will ultimately be brought against the Sinn Fein president.

Amid uncertainty about the status of the tapes still held in the archive, Boston College has now offered to return the material to those individuals who have given interviews.

Mr Adams, 65, who vehemently denies any involvement in the murder or that he was ever a member of the IRA, has denounced the oral history project, claiming many of its participants were opposed to Sinn Fein.

College spokesman Jack Dunn, in an interview with the BBC, said it was prepared to hand the relevant material to those who were interviewed.

He said: "Obviously we'd have to verify that they were the individuals that took part in the process.

"If they wanted those documents returned, we'd be prepared to return those documents."

Meanwhile, Mr Robinson said his partner at Stormont, Mr McGuinness, needed to make clear whether he had breached his pledge of office, which requires support for the police.

He asked: "Why would we leave the (ministerial) executive because Sinn Fein breaches the pledge of office?

"If Sinn Fein breaches the pledge of office,they should be put out of government."

In another twist, Mrs McConville's son Michael alleged yesterday that, a number of years ago, Mr Adams threatened him with a "backlash" if he released the names of those he believed were responsible for his mother's death.

The party leader said his sole purpose in meeting him was to help his family.

"I can understand the antipathy they feel toward republicans, given the abduction and killing of their mother and the life they subsequently had," Mr Adams said.

"However, I made no threat against Michael McConville and neither did I warn of backlash."