A 23-year-old man arrested in Derry in connection with a claim of responsibility by the New IRA following the attempted murder of Detective Chief Inspector John Caldwell has been released following questioning.

His arrest came after a typed message was posted on a wall in the city purportedly from the New IRA and claiming responsibility for Mr Caldwell's attempted murder.

Police have said the New IRA is the main line of inquiry in the investigation.

DCI Caldwall remains critically ill in hospital after being shot several times at a sports complex in Omagh last month.

The investigation continues, the PSNI said.