First the bomb attack @ Ansbach, Bavaria, Germany and a report - in an IS magazine - that the suspect:
...had fought with al-Qaeda affiliate Jabhat al-Nusra. It appears that Daleel later pledged allegiance to Islamic State of Iraq and the Levant (Isil) after the 2013 split from Nusra....he left Syria to seek treatment after he was wounded in a mortar attack. He travelled on to Germany posing as a refugee.
(From another source) He was to be deported to Bulgaria under the EU’s Dublin rules, but the move was delayed by his claims of ill health.
Link:http://www.telegraph.co.uk/news/2016...-questions-ov/

Leaving aside whether any agency could have id'd his past in Syria, there is the scale of migration into Germany in 2015, over a million people.

Second yesterday's murderer in a church in Normandy, France:
The 19-year-old was under police supervision and wore a tag following his release in March after 10 months of preventative custody for trying to go to Syria....Ordered to live at his parents’ home, he was allowed out between 8.30am and 12.30pm on weekdays, and from 2pm to 6pm on weekends. He was, therefore, within his rights to be out at the time of the attack...
Link:http://www.telegraph.co.uk/news/2016...adel-kermiche/

Taking a wider view a French-Algerian commentator:
The vast majority of the terrorists who have now slaughtered some 250 people in separate incidents across France over the past 18 months were just as well known to the authorities as Kermiche. Many were meant to be in prison, or – again like Kermiche – at least reporting to their local police stations under strict bail terms. Instead they were given more than enough freedom to move across borders and acquire the arms necessary to carry out their carnage pretty much anywhere they chose.
Link:http://www.telegraph.co.uk/news/2016...-stop-jacques/

Kermiche clearly was a "hard case" to change, but France has almost no such state capability (like Germany).