The passenger who boarded the Malaysia Airlines flight using a stolen Austrian passport was a 19-year-old Iranian who might have been trying to migrate to Germany.
He was unlikely to be a member of any terrorist group, said Malaysian authorities at a press conference on Tuesday afternoon.
The authorities have identified the teenager as Pouria Nour Mohammad Mehrdad. They said they have been in contact with the teenager's mother who had been waiting for him in Frankfurt.
The mother had known that he was travelling on a stolen passport, police added.
The police are looking at possible scenarios including hijacking, sabotage, psychological problem and the personal lives of the passengers and crew.
Officials added that a passenger could have taken out a huge life insurance and then boarded the plane.
Police said they will be releasing photos of the two who travelled on stolen passports.