Bobby Storey, a senior member of the Sinn Fein party in Northern Ireland, has been arrested on suspicion of murderer.
Storey is a former IRA commander, and is suspected of being involved in last month's murder of a former IRA member, police say. They believe that the killers wanted to take revenge for another IRA commander who was assassinated in May.
The investigation has grown quickly; Storey is the sixteenth person to be arrested.