The 55-year-old man was arrested in the Belfast area this morning under Section 41 of the Terrorism Act.
He has been taken to the Serious Crime Suite at Musgrave Police Station where he will be interviewed.
Two men, aged 24 and 29, arrested in the Derry area yesterday remain in police custody at this time.
Three men have already been charged with Lyra’s murder and another two men have been charged with rioting and associated offences on the same night.
The New IRA later claimed reponsibility the author’s murder.
She was shot dead while observing riots in Creggan’s Fanad Drive.