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Dutch police and prosecutors are questioning two suspects as they investigate whether a deadly shooting on a tram in the central city of Utrecht was an act of terror.

Police spokesman Joost Lanshage said Wednesday that officers arrested a 40-year-old man in Utrecht on Tuesday and released two other men detained earlier. The alleged shooter, 37-year-old Gokmen Tanis, remains in custody.

A man opened fire on a tram on Monday, killing two men and a woman and seriously injuring three others.

Prosecutors say they are seriously considering an extremist motive after finding a note in a suspected getaway car after the attack, and because of the nature of the shooting, but have not ruled out other possible motives.

Lanshage says, "we are looking into every lead there is."