BEDFORD, Mass. — The black boxes containing the cockpit voice recorder and flight data recorder are in the hands of federal safety investigators trying to determine the cause of a fiery weekend crash outside Boston that killed Philadelphia Inquirer co-owner Lewis Katz and six others on his jet.

National Transportation Safety Board staff retrieved the data boxes Monday evening after lowering an investigator to the burned, but intact, cockpit. The wreckage lay across a ravine off the end of a runway at Hanscom Field, a regional airport that serves mostly corporate aviation, private pilots and commuter air services.

Katz’s Gulfstream jet crashed during takeoff on Saturday night, killing him, three guests and three crew members.

Katz had gone to Massachusetts to attend an education-related event at the home of historian Doris Kearns Goodwin.