German prosecutors say an Afghan migrant held in the fatal stabbing of his 15-year-old ex-girlfriend is now suspected of murder after investigations showed he acted with "guile."

Landau prosecutors say the victim was surprised by the attack — one of the requirements for a murder charge. They had previously accused the suspect of manslaughter, which carries a lesser penalty.

The attack in a drugstore in Kandel, near the French border, has fueled debate in Germany about integration and the need to better determine migrants' age. The suspect claimed to be 15 and authorities said shortly after the attack that they had no reason to doubt he was a minor.

Prosecutor Angelika Moehlig said Tuesday the office will receive an expert report on the suspect's age "in a few weeks."