This teenager, named Bill Martin, was visiting a Civil War battlefield with his family, heard about how some soldier's wounds glowed after they sat in the mud and rain for a day or two waiting for medics, and realized that his mom had studied luminescent soil bacteria for her job. He wondered if those bacteria caused Angel's Glow, and decided to do some research. The glowing soil bacteria (Photorhabdus luminescens) lives in nematodes, which are parasitic worms that burrow into insect larvae living in the soil. The bacteria come out of the nematodes, kill the insects, and cause the corpse to glow. Then the bacteria and nematode eat the corpse until the nematode eat the bacteria again, and move to a new insect larvae, restarting the cycle. See the life cycle here.
By looking up historical records about the battles, Martin and his friend found that conditions were pretty good for the nematode and bacteria, and they may have survived in human bodies if they caught hypothermia after sitting around all night in the rain. So, if the glowing bacteria got in the soldier's wounds, it would cause Angel's Glow, and may have even competed with more deadly bacteria that would cause infections, explaining why glowing soldiers had a higher survival rate!
Super cool investigation work, and the teenagers won first place at the 2001 Intel International Science and Engineering Fair.