Dutch authorities said on Tuesday they were seriously considering a terrorist motive behind Monday's deadly shooting on a tram in the city of Utrecht.
Three people were killed and five wounded in the attack, and a 37-year-old Turkish-born man identified as Gokmen Tanis was arrested after a seven-hour manhunt.
Police said two other suspects were also in custody but their role was unclear.
"Up to this point, a terrorist motive is seriously being considered," prosecutors said in a statement, citing "the nature of the shooting and a letter found in the getaway car."
But it remained unclear whether Tanis, who has a history of run-ins with law enforcement, was acting on political beliefs or a personal vendetta. "Other motives are not being ruled out," the statement said.
He was convicted for illegal weapons possession in 2014 and for shoplifting and burglary earlier this month.
He was released from custody on March 1, after having been detained on suspicion of rape, the Utrecht District Court said in a statement released after his arrest on Monday.
Under Dutch law Tanis must be brought before a judge by Thursday but he does not yet have to be charged.
The three Dutch victims were identified as a 19-year-old woman and two men aged 28 and 49. Three others, ranging from 20 to 74 years old, were critically injured in the shooting.
Prosecutors said they had so far not been able to establish a connection between the victims and the suspected gunman.
Flags flew at half mast on government buildings across the Netherlands on Tuesday and a minute of silence was observed in the Dutch parliament in tribute to the victims.
Watch Euronews' Bryan Carter on the latest from Utrecht in the player above.