German police on Saturday arrested the suspected killer behind a knife rampage that left three people dead at a street festival, an attack claimed by the Islamic State group. The unidentified assailant fled after striking in the western town of Solingen late on Friday, sparking a day-long manhunt. “We have just arrested the true suspect,” North Rhine-Westphalia region interior minister Herbert Reul said on public television late Saturday evening. “The man we have been looking for all day has since a short time ago been in detention,” he said, adding that police found evidence to convict him. I…