Twins Alessia and Livia Schepp were taken by their father last monthAn international search for the blonde 6-year-olds, Alessia and Livia, has been under way since last month when their Swiss mother reported them missing.
And in an ominous sign, Italian authorities now say the father, Matthias Kaspar Schepp, took his daughters to Corsica - but left the French island alone.
Police spokesman Jean-Christophe Sauterel revealed that analysis of the father's work computer had turned up the new leads and the investigation is also now focusing on his behaviour before he disappeared.
"Before leaving Switzerland he researched websites for information on firearms and various methods of suicide, different poisoning techniques and ferry timetables," Mr Sauterel said.
The search for the missing girls continues"Investigations continue in Switzerland and in Italy, but are now revolving around Corsica."
Schepp, 43, was found dead on February 3 in the Italian city of Cerignola after apparently throwing himself under a train.
His Audi A6 was found parked near the station, with no child car seats or children's clothing inside.
Schepp picked up his daughters on January 30, but did not return them to their mother, Irina Lucidi, that night, or to school the next morning, as planned.
She has since made an emotional appeal for information about her daughters.
The parents, who had separated, lived in St. Sulpice, an affluent lakefront community in Lausanne, and police tracked his movement from Lausanne to France using his mobile phone signal.
He left Lausanne with the girls in the afternoon and the next day withdrew 7,500 euros (£6,300) in cash in Marseille before buying three tickets for the French island of Corsica.
Several witnesses have come forward to say they saw the twins with their father on the boat, notably in the children's play area. One witness has formally recognized the father at the port in Propriano on the morning of February 1.
Police spokesman Jean-Christophe Sauterel on the missing girls' fatherBefore leaving Switzerland he researched websites for information on firearms and various methods of suicide, different poisoning techniques and ferry timetables
Mr Sauterel said the father looked at sites about firearms on January 27 - the day he wrote a will police later found in his home and three days before he disappeared with the girls.
"Two days before he fled he looked up information about different poisoning techniques and timetables for ferries between Marseille and Corsica," Mr Sauterel said.
"The information shows that the father had planned the trip in detail."
Police are still investigating if Schepp's online research into poisons was self-directed, or aimed at his children.
:: Anyone with information on the twins has been asked to contact the investigating authorities on +41 21 644 82 31.
