Police have opened a criminal investigation after the remains of 10 fetuses and an infant were found hidden in the ceiling of a former Detroit funeral home last week. An anonymous letter led state regulators Friday to the building that housed the Cantrell Funeral Home before its mortuary license was suspended in April.

Detroit Police Chief James Craig says the department plans to open a criminal complaint on an allegation of failing to properly supervise the final disposition of a human body, a felony when in excess of 180 days. While it's not clear how long the remains were in the attic, at least one was marked with a date in October 2017, Craig said.

The anonymous letter was sent to the Michigan Department of Licensing and Regulatory Affairs, which has been conducting a civil investigation since shutting down the funeral home in April, when it found filthy conditions and 20 embalmed bodies in various states of decomposition, according to CBS Detroit. The letter led state officials to the exact location of the remains in a lowered ceiling between the first and second floor, wrapped and placed in a box and a small coffin, Craig said.

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A statement released from the Wayne County medical examiner to the Detroit Free Press says the remains were mummified. Most have some kind of identifying label from a hospital that could aid in their identification, but the process could still take weeks or months, said Wayne County Chief Medical Examiner Dr. Carl Schmidt.

"Due to the conditions of the remains, the best path toward positive identification is finding existing records," said in the statement released Tuesday afternoon. "The fact that these remains reached a funeral home means there should be a record somewhere that can help lead us to identifying information."

Craig said he couldn't speak to a motive.

"It's horrible -- I've never heard of anything like this, this is the first time in my career," Craig said. "I just can't explain it, it makes no sense."

No one is currently in custody in connection with the case. The Associated Press reports it wasn't able to find a telephone listing for Raymond Cantrell, who owned the funeral home when its license was suspended.

The building's new owner, Naveed Syed,called the discovery "gruesome." He told the AP he bought the building last month with plans to transform it into a community center.

"The priority is to find out the next of kin for all those babies. And why they did it. And what actually happened and who did it," Syed said.