The old tenants had been booted from the rental so it was time to get the place washed and scrubbed. The house — a tiny two-bedroom beige postwar cottage tucked on a residential street corner in Missoula, Mont. — was an empty eyesore last September.

“The tenants were dirty,” a neighbor would later grumble to NBC Montana. “It was an unkempt house. The yard was a mess.”

The property owner brought in a professional cleaner to tackle the job, including “a significant amount of miscellaneous items that had been left by the evicted renter,” according to a search warrant application later filed with the local courts. On Sept. 27 the crew arrived and worked through the house’s 896 square feet and the backyard, where a weather-roughened two-car garage and shed stood.

When the cleaners picked through the shed, they found a box in the building. Inside was a horrific discovery: human bones.

“Loose teeth, there was what appeared to be bone from a lower jaw, and others that were not as specifically described, but I would call them pieces of bones,” Missoula Police spokesman Sgt. Travis Welsh told KPAX. “There were also rocks in this box.”

A laboratory analysis added a layer of tragedy to the find: Not only were the remains recent, they belonged to three children: one between the ages of 5 and 8, one between 6 and 10, and the third between 2 and 4 years old.

When news of the discovery went public this week, Missoula authorities admitted they were stumped. “Nothing we’ve been able to connect them to yet,” Welsh said. “The thing is, there are missing children all over the world. And the thing is, we don’t know that this particular case is isolated to the city of Missoula.”