Co-pilot Lubitz had "serious depressive episode" six years ago

Depressed: Lubitz had suffered from poor mental health in recent years
Depressed: Lubitz had suffered from poor mental health in recent years

Police have searched the homes of co-pilot Andreas Lubitz in two German cities in search of an explanation for why he may have crashed a passenger plane into the French Alps, killing all 150 people on board.

German tabloid Bild reported today that Lubitz had a "serious depressive episode" six years ago and that a medical problem was noted in aviation records.

The Federal Aviation Office was not immediately available for comment.

French investigators believe the 27-year-old locked himself inside the cockpit and then intentionally smashed the Germanwings Airbus A320 plane into a mountainside.

Dusseldorf police spokeswoman Susanna Heusgen said "no crucial piece of evidence has been found yet" after the searches in Dusseldorf and Montabaur.

Dusseldorf prosecutors said they plan to release an update later today.

Meanwhile, Germany's president has attended a memorial service in the western town of Haltern for the 16 students and two teachers from the local high school who were among those killed.

President Joachim Gauck and North Rhine-Westphalia's state governor, Hannelore Kraft, attended the service along with students at the town's St Sixtus church.

In France, the airline, Germanwings, said it was setting up a family assistance centre in Marseille for relatives of the victims.

Chief executive Thomas Winkelmann said in a statement that "in these dark hours our full attention belongs to the emotional support of the relatives and friends of the victims of Flight 9525".

Read: Prosecutors say co-pilot deliberately brought plane down in French Alps.