German federal prosecutors have taken over the investigation into a knife attack in the western city of Solingen that left three people dead and others severely wounded, as they probe a possible Islamist motive. Police said on Saturday night that a suspect had handed himself in and admitted responsibility for the attack. A spokeswoman for the prosecutor’s office told dpa on Sunday that it was investigating the suspect on suspicion of membership of the terrorist militia Islamic State. Islamic State previously said that one of its members carried out the stabbings. Police in Dusseldorf said on S…