Since the girls' father, Matthias Kaspar Schepp, was found dead by a railway station in southern Italy on Thursday, the Swiss police say they have not turned up any firm evidence of the whereabouts of 6-year-olds Alessia and Livia since they were reported missing on Jan. 30.
Nor is anything yet certain, Swiss police in the canton (state) of Vaud said Monday, about the girls' possible trail in Switzerland, France and Italy since they spent the last weekend in January at the home of their father in the Lausanne suburb of St. Sulpice.
Authorities believe the 43-year-old Schepp, a Canadian-born resident of Switzerland who was separated from his wife, threw himself under a train. His body was found late Thursday by a railway station near the port city of Bari, Italy.
In an international search dubbed "Operation Gemelle," police in the three nations have been looking for the twin girls who lived in Lausanne with their mother, Irina Lucidi, 44. Some 40 Swiss police investigators are now on the case, said Vaud police spokesman Jean-Christophe Sauterel.
Swiss police said Monday that French police in Marseilles had established that Schepp bought tickets for himself and his daughters to catch a ferry to Propriano, in Corsica, but they were unable to determine whether they had boarded it.
Swiss police have been searching the parents' homes several times and canvassing the neighborhood of St. Sulpice, talking with people in 60 different homes along the affluent lakefront community that is home to a well-known 12th-century Roman church.
They examined four boats in the nearby ports of Morges and Vidy along Lake Geneva and gas stations between St. Sulpice and Geneva, about 50 kilometers (31 miles) away.
A helicopter Monday swept over the lake.
"For now, these controls have failed to track down the two girls," Sauterel said in a statement.
Schepp had picked up his daughters from their mother's home on Jan. 28 for the weekend. Alerts for the missing girls went out throughout Europe two days later.
Police said Sunday they believe Schepp drove the girls in a Swiss-registered Audi A6 black wagon through Annecy, France, and to Marseille last week, and they checked for any speeding tickets or records from customs checks along the Swiss-French border.
The headmaster at the school in St. Sulpice met with students and teachers Monday morning to reassure the other children.
Both of the missing girls have been described as wearing glasses and blue jeans, with Alessia dressed in a white jacket over a striped shirt and Livia dressed in a purple ski jacket over a green T-shirt. Authorities have urged anybody with information to come forward.