Fire crews were called to the derelict site five times over just two days.
The derelict building that once housed St Mary’s Youth Club went up in flames on Saturday night.
The suspects managed to escape with a cash box containing money.
Derry City suffer their first home defeat of the season as Dundalk clinch a deserved 2-0 win at the Brandywell.
The pedestrian, who was in his 80s, was struck on Derry’s Crescent Link