STERLING HEIGHTS, Mich. -

For the third time in just more than a year, crews working on a 13-foot diameter sewer interceptor in Macomb County have found human body parts.

Three small pieces of what police call "fatty flesh" were found Wednesday morning. The crews were working deep below ground near 15 Mile Road and Maple Lane in Sterling Heights.

Investigators say they are leaning toward a theory that the pieces are being illegally disposed by a medical facility. They are roughly 1 inch thick and 3 or 4 inches across.

"We've checked with the medical profession,” said Sterling Hts. Police Lt. Kevin Reese. “It is somewhat consistent with medical procedures -- plastic surgery or weight loss surgery.”

Reese also points out that no missing women have been reported who could be linked to the case. Also, no one has recognized pictures of tattoos released after other body parts were found in the same area last year.

The sewer runs into northern Macomb and Oakland counties, so discovering where the material went into the system will be extremely difficult. The pieces are small enough to have been flushed down a toilet.

Investigators will do a DNA analysis, and try to match it with DNA databases.

Tests of body parts found in Sterling Hts. in August of 2012, and in Warren in December of 2012, show they came from two white females.

The last pieces are also from a white person.