An interesting note here from a NY Times article on the case regarding the van as a “stolen” vehicle:
Josh Taylor, a spokesman for the department, said the police had no reason to arrest Mr. Laundrie, who returned to Florida in the van, which was registered to Ms. Petito and has not been reported stolen.
“The reality of that situation is that it was a common-use vehicle between the two of them,” Mr. Taylor said. The state law does not allow the police to arrest Mr. Laundrie any more than it allows for the arrest of a teenager found driving his or her parents’ car, he said.
ETA: I had been wondering by the police had not used the van as a pretext to arrest or bring him in for questioning.