The Sinn Féin president was questioned for four days at Antrim police station by detectives investigating the 1972 murder of Belfast mother-of-10 Jean McConville.
Police Service of Northern Ireland chief Matt Baggott said it would have been wrong to treat Mr Adams any differently from anybody else.
Sinn Féin 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 had been on the verge of putting a motion before the power-sharing Assembly calling for Sinn Féin’s exclusion from the ruling Executive.
Mr Robinson said he stopped short of the move when Sinn Féin “corrected” its position — a reference to Mr Adams’s statement of support for the PSNI upon his release from custody on Sunday.
Mr Baggott refuted any suggestion that there was a “dark side” to policing. He said that, under reforms to the police force which faced paramilitaries during the North’s 30-year conflict, the Royal Ulster Constabulary, there were numerous ways in which policing concerns could be addressed.
They included the Human Rights Commission, the Policing Board, made up of political and independent members, and an ombudsman who investigates complaints.
Mr Baggott said decisions on whether or not to prosecute were made independently by the Public Prosecution Service.
The director of an oral history project on the Troubles — part of which was relied upon by police to question Mr Adams — has rejected any suggestion it was set up to “get” the Sinn Féin president.
New York-based Irish journalist Ed Moloney 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 Féin, 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.”
In another twist, Ms McConville’s son Michael alleged 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.
Mr Adams said his sole purpose in meeting him was to help his family.
“I made no threat against Michael McConville and neither did I warn of ‘backlash’,” he said.