A bank robber on Long Island may soon be caught red-handed — since the dye pack in his loot exploded as soon as he left the location.

The pack filled with red ink went off outside a TD Bank branch on Route 112 in Medford shortly after the thief held up the location, threatening a teller with violence.

The thief is described by cops as a white, middle-aged man who is about 5-foot-8 with a medium build.