They used a high dose of antibiotic to kill the native gut bacteria and then fed those mice fecal material from a protected strain.

Even though fill material is mechanically compacted during site preparation it doesn't drain as well as native slopes.

"I'm a scientist, and it means I regret that important material is getting reburied, " he said. "But when you find that these remains are genetically Native Americans, it's not our call anymore.