European police expanded the search for twin girls whose Canadian-born father apparently killed himself last week in Italy.
Matthias Kaspar Schepp picked up his six-year-old twin daughters -- Alessia and Livia -- from their mother's house in western Switzerland on Jan. 28.
Two days later, the 43-year-old Schepp failed to return his daughters to the custody of his estranged wife, Irina Lucidi.
The girls were reported missing that same day and police across Europe began looking for them.
A police investigation has since determined that Schepp drove his daughters into France in the following days, where they were seen in the seaside city of Marseille on Feb. 1. While in Marseille, Schepp sent a postcard to Lucidi.
Schepp was last seen alive in Italy. His body was found Feb. 3 near the port city of Bari and police believe he threw himself under a train.
It is not clear if Schepp brought his daughters with him to Italy.
An international search dubbed "Operation Gemelle" is taking place in all three countries. Some 40 Swiss investigators are on the case.
Investigators have examined four boats along Lake Geneva and gas stations between St. Sulpice and Geneva, a 50-kilometre stretch.
On Monday, a helicopter hovered over the lake.
"For now, these controls have failed to track down the two girls," Vaud police spokesman Jean-Christophe Sauterel said in a statement.
Italian police official Alfredo Fabbrocini said authorities are still trying to work out all the details of Schepp's final days, by examining any cash withdrawals and phone calls he may have made.
"There's a gap of a few days," Fabbrocini told The Associated Press on Sunday.
A Facebook page called "Missing Alessia & Livia" urges anyone with "serious information" about the case to contact authorities.
Many Facebook users have posted comments expressing hope for a safe return of the twin girls, but also concern about what may have happened to them.
A woman named Eve Koyanagi, who described herself as a worried mother from Toronto, wrote Monday that the case has to be a parent's "worst nightmare."
With files from The Associated Press
