A group of people walking on a North Philadelphia street came across the casket around 9 p.m. Monday, lying on a sidewalk across the street from a cemetery.
"I was pretty shocked," witness Chris James told the station. "It looked like something straight out of 'Thriller.'"
James told the station the group didn't open the casket, but instead contacted authorities.
"We didn't want to open it," James said. "We didn't know what was inside. We didn't know if toxic waste could be in there, anything, we honestly thought it could be an animal."
James described the coffin to Philly.com as a "small casket wrapped in a trash bag," and when officers opened it, James said they found a black plastic bag with dirt and "something organic" inside.
"It did look like organs," James told Philly.com.
Philly.com reports investigators don't know where the remains came from.
"According to the medical examiner, [they] were in fact human organs. They believed they belonged to an infant or a child," Chief Inspector Scott Small told CBS Philly. "What's unusual is inside the coffin, other than the bag of organs, there was no body."
Small said the casket was "fresh" and recently pried open. Investigators are looking into whether someone stole it from an area funeral home or if it was dug up from a cemetery, including Mt. Vernon directly across the street from where the casket was found.
MORE: Read more at CBSNEWS.com