During the Battle of New York, some Chitauri forces managed to corner a large group of civilians, including Beth, inside a bank, and they intended to detonate one of these explosives to obliterate the hostages.
A deleted scene titled "The Cop and the Waitress" shows when placed in captivity, Beth stumbled upon a pair of glasses and a watch. Her expression became horrified as she realized the Chitauri had already killed a group of civilians they had imprisoned in the bank by vaporizing them with a Chitauri Bomb, and were intending to do the same with her group.
Captain America went to the bank to rescue the civilians, and while fighting the Chitauri soldiers, one of them launched the explosive at Rogers at short range in a kamikaze attack. Captain America was able to defend himself from the blast with his own shield, saving the civilians in the process.