Federal investigators have concluded that thieves armed with detailed shipping information were behind the removal of a Goya painting from a truck en route to the Solomon R. Guggenheim Museum from Ohio last week, law enforcement officials said Friday. 

The 1778 painting, “Children With a Cart,” was packed inside several nested crates aboard a locked unmarked truck used by a professional art transporter. The crated painting was removed from an outer shipping container in the truck while it was parked at a Howard Johnson Inn near Bartonsville, Pa. 

The two drivers checked into the hotel around 11 p.m. on Nov. 7, according to the motel manager, Faizal Bhimani. He said the white midsize truck was left in an unlighted parking lot adjacent to the hotel, out of sight of the hotel’s rooms and the main office. 

When the drivers returned to the truck at about 6:30 a.m. on Nov. 8, the locks had been broken and the painting, insured for $1 million, was gone, law enforcement officials said, speaking on condition of anonymity.

Robert K. Wittman, former head of the FBI's Art Crime team and now a security consultant in Philadelphia, notes that history's most infamous art thefts, including the 1990 Isabella Steward Gardner Museum heist in Boston, targeted works hanging on walls, not in transit. But he adds that art on the move is at its most vulnerable. 

Mr. Wittman helped recover a 1778 Goya masterpiece stolen off a truck in Pennsylvania in 2006 en route from the Toledo Museum of Art in Ohio to the Guggenheim in New York. In that case, its two drivers made the dumb decision to check into a motel for a nap. They returned to find their parked truck busted open and the unmarked Goya crate gone. The thief didn't know what he had, and said he wanted to get rid of it. He didn't destroy the painting because "it kind of grew on me." He had a lawyer contact authorities saying he had found it in his basement—there was a $50,000 reward—but wound up pleading guilty and being sentenced to five years in prison.