Ukrainian brothers charged with slave labor in Philadelphia

To keep the workers in line, the brothers allegedly used "slapping, punching, and kicking," and death threats, the documents said.

After some workers escaped, the brothers "resorted to . . . threats to the workers' families in Ukraine," according to the documents. One worker was told an 8-year-old daughter in Ukraine would be turned into a prostitute.

The brothers traveled back to Ukraine in 2007 in an attempt to collect money by threatening the migrants' families, officials said.

The investigation was conducted by the U.S. Attorney's Office, the FBI, Immigration and Customers Enforcement, and state and local police.

It started in 2005 with a tip from overseas, but was slowed because of language barriers, fear, and a mistrust of American police after experiences with law enforcement in other nations, Lindquist said.

Contributing to this article were Inquirer staff writers Troy Graham, Julia Terruso, and Sam Wood.