One of the Brussels suicide bombers was detained last summer on suspicion of being an Islamic State fighter, but Turkish authorities sent him on the path toward freedom after their Belgian counterparts couldn’t establish that he had any link to terror groups.

The revelation Wednesday from Turkish President Recep Tayyip Erdogan was the latest in a string of miscues that has plagued Europe’s efforts to crack a terror network that has killed more than 160 people in two of the continent’s capitals in the past four months.

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