Pursuing substantial evidence

German authorities are pursuing substantial evidence that the perpetrator of Wednesday's attack at Frankfurt Airport, which killed two American airmen, had links with Islamist groups in Germany. There is concern that additional attacks may be in the works.

Following initial investigations, security authorities in Germany are investigating whether Wednesday's shooting at Frankfurt Airport was a targeted attack on the US Army. They are also exploring whether US soldiers in Germany are at risk of further attacks.

Ok, here is a clue. The shooter was a devout Muslim (according to his family and those who knew him) And he was shouting God is great! in Arabic while executing Americans. So the authorities are pursuing substantial evidence that he 'had links to Islamic groups?

There in lies the problem.....