Hayes said investigators were unsure of the cause of death and weren't identifying the victim.
A potentially disturbing story line had emerged earlier in the evening, according to a law-enforcement source.
The victim appeared to be a man who was reported missing by his family earlier in the day in Northeast Philadelphia's 15th District, the source said.
The family claimed to have received a threatening phone call from someone who was holding their relative for ransom, the source said.
Hayes, however, said it was unclear if the decomposed body was that of the man who had been reported missing.
The investigation, he noted, was still in the early stages.
As of 9 last night, investigators were still at the scene on Hope Street, a block barely wide enough to fit a cop car.
"Anything could go on out here," said Campbell, who lives in one of the two occupied houses on the block.
About five years ago, he said, a dead body was found stuffed in a container in a weedy lot next to his house.
Janis Bossert, whose house is situated behind the lot where the body was discovered, said she has two video cameras monitoring the area outside her house.
Police were examining her surveillance footage to see if someone had dropped the victim's body in the lot, which runs alongside a graffiti-covered brick building.
"It's a nice neighborhood," Bossert said, "but now I'm thinking back to last night, when I was out bringing in groceries by myself."