Two teenagers taunted a man rummaging through a trash bin and then killed him after he bared his buttocks at them, police said Tuesday.

"He didn't want to be harassed by these kids or whatever and he mooned them," Upper Darby Township Police Sgt. David Madonna said.

Christopher McEneaney, 16, and Andre Mark, 18, were charged Monday in the slaying Friday night of Martin Malone, 47. He was stabbed with a multi-tool and bludgeoned with a shovel.

Police said the teens were walking through an apartment complex just outside Philadelphia when they saw Malone picking through the trash and began calling him a "bum" and other names, Madonna said. Malone responded by exposing his buttocks.

The teens threw rocks at him and then attacked him, leaving him to die in a field, police said.

Police arrested the two after witnesses described the clothing the attackers were wearing.

Malone had lived with his sister, Molly Munsell, for about a year.

"He didn't deserve what happened to him," Munsell told the Philadelphia Daily News. "He was just one of those people who minded his own business."

A call to the prosecutor's office to determine if the teens had lawyers was not immediately returned.