Six people on flight, including journalist, remained in Belarus.

At least six people who boarded the Ryanair flight in Athens were not on the plane when it finally arrived in Vilnius, Lithuania, the police commissioner of Lithuania said on Monday.

Among the six were the dissident journalist Roman Protasevich and his girlfriend, Sofia Sapega, who were both detained.

The identities of the other four people who apparently got off the plane after it was forced to land in Minsk, Belarus, on Sunday are not publicly known — and are being investigated by the Lithuanian police.

“What I know is that six people did not arrive in Vilnius,” Renatas Pozela, Lithuania’s police commissioner general, said in a telephone interview with The New York Times.

Further details, he said, “are being looked into as part of the criminal investigation.”

The Lithuanian police opened a hijacking and kidnapping investigation into the forced landing of the plane, and they questioned the pilots after they landed in Vilnius on Sunday evening, Mr. Pozela said.

Police investigators are interviewing the passengers this week, he said.

“The pilots were the priority,” Mr. Pozela said. “We wanted to hear their stories. How did they see the situation? What did they do? Were there other planes?”

Mr. Pozela said he was not yet authorized to disclose any findings of the investigation.