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Floral tributes are left at the scene of the terrorist attack where a truck crashed after driving down a pedestrian street in downtown Stockholm on April 8, 2017 in Stockholm, Sweden.

The man suspected of ramming a stolen truck into a crowd in Stockholm on Friday and killing four people was an Uzbek asylum-seeker whose application was rejected and was supposed to be deported. He was given four weeks to leave the country in December but could not be located because he had given police a wrong address. Although the suspect’s request for asylum had been rejected in June 2016, police didn’t formally start looking for him until Feb. 24.

A second person was also arrested, "suspected of terror crimes through murder,” according to Sweden’s prosecutor’s office. "He is suspected on reasonable grounds, which is the lower degree of suspicion. The other individual is suspected with probable cause, the higher degree of suspicion.”

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Police patrol a pedestrian mall in Stockholm on April 8, 2017, the day after a hijacked truck plunged into a crowd in a pedestrian shopping area.

As thousands gathered near the site of the attack to show support for the victims, officials revealed the suspect had expressed “sympathy for extremist organizations.” Swedish Prime Minister Stefan Lofven has said the attack that killed two Swedes, one Belgian, and one British national was “an act of terrorism.” Fifteen people were injured, 10 of whom were still hospitalized as of Sunday.

News that the man suspected of driving the beer truck into a crowd of people was an asylum seeker “is almost certain to inflame debate in Sweden over the country’s relatively welcoming attitude toward refugees,” notes the Washington Post. It is also a stark reminder of how difficult it is for authorities to stop these types of attacks that are becoming increasingly common across the continet. Last month, a man plowed his car into a crowd in London, killing five people, only months after 12 were killed in Berlin when a truck rammed into a Christmas market in Berlin.