Germany’s opposition leader has pledged to strengthen border controls and step up deportations if he becomes chancellor after elections next month, a day after an Afghan man was arrested over a knife attack in which two people died.

Friedrich Merz, whose conservative CDU/CSU alliance is leading in polls, said he would not allow attacks like the one in the Bavarian city of Aschaffenburg on Wednesday to become a “normal affair”.

The suspect in the attack, who was arrested shortly afterwards, is a 28-year-old Afghan man with a history of psychiatric problems and violence. The man’s asylum process had been closed at his request after two years, according to Bavarian authorities. He had said he would leave Germany of his own will last month, but had not done so, and had continued receiving psychiatric treatment.