The Chief Constable of the Police Service of Northern Ireland Matt Baggott today hit back at Sinn Féin criticism regarding arrests by his officers investigating the murder of one of his officers.
Deputy First Minister Martin McGuinness questioned the detention of a 22-year-old man in Coalisland, Co Tyrone, who has since been released by police.
Constable Ronan Kerr, 25, was killed when a booby-trap bomb exploded under his car outside his home in Omagh, Co Tyrone, on April 2.
Mr Baggott said: "The investigation into the murder of Ronan Kerr, and other very serious associated crimes, is complex and will take considerable time to complete.
"It is being conducted under the law and future charges remain the responsibility of the independent Public Prosecution Service. Any comment is therefore premature.
"My assurance is that the investigation will remain methodical and relentless and will continue to be absolutely impartial and completely free of political influence."
Detectives investigating the murder, as well as what police described as "associated incidents", arrested five men ranging in age from 22 to 46 on Tuesday.
The operation, which included searches at a number of locations and involved 200 officers, was followed yesterday by the arrest of a 23-year-old woman.
After police confirmed the release of the 22-year-old man who had been detained in Coalisland, Mr McGuinness issued his broadside against the investigation.
The Sinn Féin Mid Ulster MP said: "I know the family of the young man arrested yesterday in Coalisland. It was claimed by the PSNI that the arrest and search operation at his family home was in connection with the murder of Ronan Kerr."
Mr McGuinness said the arrest featured prominently in the media and added: "The young man who was arrested and subsequently released today was in the USA at the time of that murder and was in no way involved in it."
The Deputy First Minister said: "People are in no doubt where I stand in relation to the killers of Ronan Kerr. I believe that the PSNI have a duty to properly investigate this murder.
"However the arrest and release of this young man raises very serious questions about the quality of the current PSNI investigation.
"Bad policing operations in republican communities will do nothing to bring his killers to justice. Indeed if anything the opposite is the case."