Mike MacQueen hunts for war criminals and has spoken to dozens of them.
The US investigator worked for many years tracking down Nazi death camp workers who'd escaped to America and, since 2008, has focused on Bosnian war crimes.
The job involves sifting through enormous amounts of information collected by authorities in Bosnia, pulling out names mentioned by witnesses and victims and checking them against immigration data in the US.
Officials there are now planning to deport more than 100 Bosnians suspected of commiting atrocities.
One of them, Almaz Nezirovic, is accused of working at a death camp in 1992, where he tortured prisoners.
Mr MacQueen came across his name in witness statements while sifting through police records in Serejevo.
Nezirovic become one of the many war criminals the investigator has interviewed.