DUESSELDORF, Germany - The personality of a co-pilot suspected of deliberately flying a Germanwings passenger jet into a mountainside in the Alps is a "serious lead" in the inquiry but not the only one, a French investigator said Saturday.
"We have a certain number of elements which allow us to make progress on this lead, which is a serious lead but which can't be the only one," police chief Jean-Pierre Michel told AFP in the western German city of Duesseldorf.
The investigation so far has not turned up a "particular element" in the life of co-pilot Andreas Lubitz which could explain his alleged action in the ill-fated Airbus plane, he added.
The black box voice recorder indicates that Lubitz, 27, locked his captain out of the cockpit of the Germanwings jet and deliberately flew Flight 4U 9525 into a mountainside, French officials said.
German prosecutors believe Lubitz hid an illness from his airline.
They said Friday that searches of his homes netted "medical documents that suggest an existing illness and appropriate medical treatment", including "torn-up and current sick leave notes, among them one covering the day of the crash".
They did not specify the illness but media reports say he was severely depressed.
The French investigator is part of a three-strong team which has travelled to Duesseldorf to co-operate with German authorities.
"We're going to try to understand what in his life could have led him to the carrying out of the act," Michel said.