Authorities in Mauritania said Tuesday they were searching for three former members of a local terror network who fled south toward neighboring Senegal after a brutal Christmas Eve attack that killed four picnicking French tourists. Gunmen opened fire on the tourists Monday near Aleg, a small town 245 kilometers east of Mauritania's capital, Nouakchott, police said. Though authorities initially thought the family had been robbed, subsequent investigations have shown they were not, the Interior Ministry said in a statement Tuesday. The dead included two children. The sole survivor, the family's father Francois Tauler, was seriously injured and flown overnight to the main hospital in Senegal's capital, Dakar, where he was in an intensive care unit, said Moussa Samb, spokesman for the hospital. Police said they detained one man early Tuesday who allegedly arranged a taxi for the three suspected men after the attack. The taxi carried them from Aleg to Boghe, a town on the Senegalese border about 65 kilometers to the south. A taxi driver interviewed by police also said he took the three to the border town.