Updated

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

National Transportation Safety Board staff retrieved the data boxes Monday evening after an investigator was lowered to the cockpit. The wreckage lay across a ravine off the end of a runway at Hanscom Field in Bedford.

At the crash site, tire marks were visible where the Gulfstream IV jet ran off the runway, burst through a chain-link fence and toppled part of a runway lighting system.

The cockpit was burned but mostly intact, with the nose resting on a hill, and the burned-out fuselage lying in the ravine.

NTSB investigator Luke Schiada said Monday that recovering the boxes was their focus, but the team was still assembling a variety evidence, including maintenance records, crew medical records, airport surveillance video, and witnesses' accounts.

Local police released some 911 calls in which neighbors described a loud explosion and towering column of smoke. One caller Saturday night said it looked like "an atomic bomb went off" and described "a mushroom cloud" of smoke and fire.

Schiada said the pilot had 18,500 hours of flight experience and the first officer had 11,200 hours.

The chief pilot was James McDowell, of Georgetown, Delaware, authorities said. Spouses identified two of the crew members Monday as flight attendant Teresa Benhoff, 48, of Easton, Maryland, and co-pilot Bauke "Mike" de Vries, 45, of Marlton, New Jersey.

The other victims were identified earlier as Katz's neighbor at the New Jersey shore, Anne Leeds, a 74-year-old retired preschool teacher he invited on the trip just that day; Marcella Dalsey, the director of Katz's son's foundation; and Susan Asbell, 67, the wife of a former New Jersey county prosecutor.

The trip would be the last of many over the years the flight crew took with Katz; all three had worked for him for 10 to 15 years, relatives said. They had been expecting to take Katz, a sports team owner-turned-philanthropist, to France later this month, said Benhoff's husband, Dan.

The co-pilot, de Vries, had come to the U.S. from the Netherlands as a young man to attend flight school. In the early 1990s, he was a passenger in a two-man crash that killed a pilot at a southern New Jersey airport, his wife, Shelly, said.

"Lucky for him, he didn't remember it, and he didn't remember about 12 to 24 hours before it," she said.

So he had no fear, she said, and still loved to fly.

Katz had gone to Massachusetts on Saturday to attend an education-related event at the home of historian Doris Kearns Goodwin. He often would take spur-of-the-moment trips, and his crew was at the ready. Benhoff said his wife was on call all day, every day, and they spoke throughout the day Saturday.

"She loved to fly," he said. "She trusted that airplane."

Benhoff loved working for Katz, her husband said, and had gotten to know Katz's late wife, his children and grandchildren during their vacations, business trips and flights to and from family homes in Philadelphia; Palm Beach, Florida; the New Jersey shore; and New York.

The family of McDowell, the chief pilot, declined to comment.

Katz, 72, made his fortune investing in parking lots, billboards and the New York Yankees' cable network. He once owned the NBA's New Jersey Nets and the NHL's New Jersey Devils and in 2012 became a minority investor in the Inquirer.

Less than a week before the crash, Katz and Harold H.F. "Gerry" Lenfest struck a deal to gain full control of the Inquirer as well as the Philadelphia Daily News and Philly.com by buying out their co-owners for $88 million.

A public memorial service for him was planned for Wednesday at Temple University in Philadelphia, where Katz was an alumnus and trustee.