A 45-year-old man has been charged with murder over the death of a prison officer in Northern Ireland after a bomb exploded beneath his van.

Christopher Robinson had previously been charged with attempted murder in the case of Adrian Ismay. Police said Friday the charge was changed to murder after 52-year-old Ismay died earlier this week of a heart attack linked by investigators to injuries suffered during the March 4 bomb attack.

The New IRA faction claimed responsibility for the bombing and threatened more attacks on prison employees. The group, which opposes the peace process, seeks better treatment for its many convicted members.

It had also claimed responsibility for the November 2012 fatal shooting of another prison guard.

Robinson is scheduled to appear in court Friday.