Top federal and regional security officials met seven times to discuss the potential danger posed by Tunisian migrant Anis Amri in the year before he attacked a Berlin Christmas market, the latest revelation in a string of mishaps that failed to prevent the attack.

The new details, disclosed by security officials at a regional parliamentary hearing Thursday, suggest that German security and intelligence authorities miscalculated the immediate threat that Amri presented. Despite extensive surveillance, efforts to detain him repeatedly faltered because police and prosecutors believed they didn’t have evidence that would stand up in court, the officials said.

The emerging affair is raising questions about the ability of Germany, which was struck four times by Islamist terrorists last year, to prevent future attacks. It is also increasing pressure on Chancellor Angela Merkel amid accusations that her decision to accept hundreds of thousands of mostly Muslim migrants in 2015 might have put the country at risk.

“Does one have to sit in a truck before the state can act?” Social Democrat Andreas Bialas asked at one point in the nearly five-hour hearing in the parliament of North Rhine-Westphalia, echoing the public’s stupefaction at the series of revelations about why the state failed to stop Amri despite all it knew about him.

A recent Insa poll conducted for the German daily Bild found just under a fifth of those surveyed trusted Ms. Merkel’s Christian Democrats to protect the country from further attacks; Other German parties scored even lower. Germany’s interior minister, meanwhile, proposed this week revamping Germany’s decentralized security apparatus to close the gaps exposed by the Berlin attack.

“Nobody understands how a known extremist was able to walk around freely in this country,” Gregor Golland, a regional lawmaker from the Christian Democratic Union, said before questioning security officials Thursday.

The illegal Tunisian immigrant—his asylum request was rejected in June 2016—rammed a truck into Christmas market in central Berlin on Dec. 19, leaving 12 people dead and dozens more injured. He escaped after German police first arrested the wrong man and then missed crucial evidence identifying Amri in a first sweep of the truck. Amri trekked across Europe and was eventually shot by Italian police four days later.

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