PHILADELPHIA (AP) -- A trial is getting under way in federal court to determine the dollar amount two vessel operators may have to pay following a collision of a tugboat-guided barge and a sightseeing boat two years ago in Philadelphia that left two Hungarian students dead.

Sixteen-year-old Dora Schwendtner (SHVENT'-ner) and 20-year-old Szabolcs (ZAB'-ultch) Prem died when a city barge pushed by a tug slammed into their disabled tour boat on the Delaware River in July 2010.

The crash also dumped 35 others aboard the amphibious duck boat into the river.

The victims' families have sued the city, the operators of both vessels and others. They are expected to be in court when the trial starts Monday.

The pilot of the tug boat was sentenced in November to a year in federal prison.