By Q Radio News
The PSNI says it believes it knows who murdered journalist Lyra McKee.
However, the man leading the murder inquiry, Detective Chief Superintendent Raymond Murray told the BBC it was incredibly difficult to prove.
29 year-old Ms. McKee died while observing a riot in the Creggan estate in April last year.
Meanwhile, the Police Ombudsman is investigating a complaint from Lyra’s family concerning the security operation on the day of the killing.