Northern Ireland's most senior police officer has defended his force's actions after Sinn Fein criticised arrests linked to the murder of one of his men.
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. The former suspect's lawyer claimed there was insufficient evidence.
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.
Chief Constable Matt 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."
Catholic Constable Kerr's death prompted cross-community sympathy, with Gaelic Athletic Association (GAA) members of his home village of Beragh near Omagh helping police carry his coffin in a public sign of unity.
Mr McGuinness led condemnation of dissident republicans blamed for the killing. Sinn Fein has supported the police service and takes an active role in its oversight.
On Wednesday, he voiced some of his fiercest criticism of the force for many years. The Mid-Ulster MP said: "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. 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."
Detectives investigating the murder and associated incidents arrested five men ranging in age from 22 to 46 on Tuesday and later released them. The operation, which included searches at a number of locations and involved 200 officers, was followed on Wednesday by the arrest of a 23-year-old woman.