French police were warned that Brussels shooting suspect Mehdi Nemmouche posed a danger to European security after spending time in Syria, but failed to act on the intelligence before the May 24 shooting that left four people dead, according to a report in the weekly French news magazine Le Nouvel Observateur.

According to the report, Nemmouche was spotted at the airport in Frankfurt by the German police on March 18 on his way back from Syria, who allegedly warned their French counterparts that Nemmouche was labeled a "danger to national security."

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The French Interior Ministry denied the report.

Nemmouche, a 29-year-old French citizen, was detained on Friday in Marseille for the May 24 shooting at Brussels Jewish Museum that resulted in four deaths, including two Israelis.

According to an earlier report by French radio network RTL, the arrest resulted from a random drug-related check at Marseille’s bus terminal.

Reuters and JTA contributed to this report.

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