Michigan's Unidentified Chunks of Sewer-Flesh:
From 2012-2013, there were at least three cases of human flesh being found in the sewage system of Macomb County, Michigan.
The first time happened in August of 2012 in Sterling Heights, and included 10-12+* pieces of fat, muscle tissue, and skin that also featured sections of the victim's tattoo. The victim themself was an unidentified Caucasian, obese female who was estimated to have been between 15-20 years-old when she was killed, and was not in missing person's data base either. Nothing else is known.
The second time was in December of the same year around the town of Warren, and in this instance the chunks were neatly cut cubes about four inches big that included the fat, skin, and muscle tissue just like the previous case, but no identifying marks, or tattoos were present. They were found about five-seven** miles from where the other pieces had been located, and despite the similarities, the remains were determined to have come from a different victim who was also not in the missing person's data base. Yet again, nothing else is known.
The third time happened in September of 2013, and were discovered once again in Sterling Heights. The pieces were again similar in size, and style to the previous ones although they again contained no identifying marks, or tattoos like the first ones did. The victim was confirmed to have been again Caucasian, and possibly also have dark hair, but other than that just like the two other instances nothing pertaining to the victim has been released, or is known.
The two most common theories are that it's either the workings of a serial killer, or improperly disposed of medical waste from a lab, but whatever it is, the fact remains that despite ten years having passed, no leads, suspects, or identifications have ever occurred.
*Articles vary on how many pieces were actually found.
**Articles vary on the exact distance of the location.
Was there just an underground poisoning ring going on in the 80s or what??
It's never been clear as to why. Theories range from it just being some guy fucking around to the government deliberately doing it to see how a potential attack like this would pan out to a rogue employee trying to prove a point, or get back at the company to a genuine accidental contamination, etc.
Personally, I have no clue.