The father of missing twin girls trawled the internet for information on firearms, poisons and suicide days before he apparently killed himself in Italy, police in Switzerland said.
An international search for six-year-olds Alessia and Livia has been under way since January 30, when their Swiss mother reported them missing.
Police spokesman Jean-Christophe Sauterel told reporters that analysis of the father's work computer had turned up the websites, which also included ferry timetables.
Matthias Kaspar Schepp, 43, was found dead in the Italian city of Cerignola, east of Naples, on February 3.
Police believe he threw himself under a train. His Audi A6 car was found parked near the station, with no child seats or children's clothing inside.
Mr Schepp had been given custody of his daughters for the weekend, but did not return them to their mother, Irina Lucidi, as planned. The couple, who had separated, lived in St Sulpice, a wealthy lakefront community in Lausanne.
The search for the girls spread to Corsica and southern Italy on Wednesday after authorities confirmed that Mr Schepp had driven them as far as the French port of Marseille where they boarded an overnight ferry for the island of Corsica on the evening of January 31.
Alfredo Fabbrocini, a Foggia police official in charge of the Cerignola end of the inquiry, said that Mr Schepp sailed alone back to the port city of Toulon in mainland France on February 1. He then drove into Italy from France.
However, Mr Fabbrocini could not confirm Italian news reports that a camera had photographed Mr Schepp's car licence plate as he drove through the Italian coastal town of Ventimiglia, near the French border.
Mr Sauterel said Mr Schepp had looked at sites about firearms on January 27 - the day he wrote a will which police later found in his home - and over the next two days researched "various means of suicide, different techniques of poisoning and ferry schedules between Marseille and Corsica".