A deadly knife attack on a play school group in Germany, where an Afghan man was arrested at the scene, reignited a bitter immigration debate on Thursday, a month before elections.

Friedrich Merz, the conservative front-runner in the race for Germany’s chancellorship, called for a radical overhaul of the country’s migration policy including permanent border checks. The comments come after an asylum seeker from Afghanistan was taken into custody over a fatal stabbing of a two-year-old child and a man in a park on Wednesday.