It wasn't uncommon to find a dozen Marshallese mothers on the verge of giving birth in one house northwest Arkansas, said Duane Kees, the U.S. attorney for the western district of Arkansas.

"Many of these mothers described their ordeal as being treated like property," Kees said at a news conference Wednesday. "Make no mistake: this case is the purest form of human trafficking."

After giving birth, the women would then be flown back to the Marshall Islands or to another U.S. state, most commonly Arkansas, which has one the largest concentrations of Marshallese immigrants in the U.S., authorities said.

Petersen charged $25,000-$40,000 per adoption and brought in about $2.7 million into a bank account he gave families for adoption fees in less than two years, according to Utah court documents.

The Utah investigation started with a call to a human-trafficking tip line in October 2017. Staff at several hospitals in the Salt Lake City area who would eventually report an "influx" of women from the Marshall Islands giving birth and putting their babies up for adoption.

The mothers were accompanied by the same woman, who told one social worker that she goes to the Marshall Islands to "find pregnant women to adopt their babies out."