Authorities in the Netherlands are investigating the possibility that there was a terrorist motive behind the killing of three people on a tram on March 18.
Prosecutors said that they found a letter in the car used to escape by suspect Gokmen Tanis.
The 37-year-old Turkish-born man was arrested after a 7-hour manhunt in the city of Utrecht.
Two other suspects aged 23 and 27 have also been arrested, police said, but it is unknown what part they may have played in the shootings.
“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.”
However, Tanis may have been motivated by personal reasons, not politics, police said.
“Other motives are not being ruled out,” they said in the statement.
Tanis had a known criminal history, according to local broadcaster RTV Utrecht, including a shooting incident in 2013.
He was detained earlier this month on suspicion of rape but was released on March 1, the Utrecht District Court said in a statement.
Tanis is due to face the rape charge in July, the court said.
Dutch law stipulates that he be brought before a judge by Thursday, March 21 but does not necessarily have to be charged.
One local businessman told BBC Turkish that Tanis had in the past fought in the Russian republic of Chechnya, a well-known jihadist haven.
“He was arrested because of his connections with [the ISIS terrorist group] but released later,” the businessman said, according to the BBC.
Prosecutors are yet to find a link between the victims, a 19-year-old woman and two men aged 28 and 49, and Tanis.
Three other people were critically injured in the shooting, which took place in a quiet residential neighborhood known for its sizable immigrant community.
Mahmut Tanis, an uncle of the suspect who lives in the Netherlands, told Turkish media that he doubted Tanis had a terrorist motive.
“Looking at my nephew’s condition, the possibility that what he did was a terror attack is low,” he said, according to Reuters, but added that he had not seen him in years.
Utrecht is a picturesque city with around 340,000 residents. It went into lockdown following the shooting.
Mosques, schools, and local universities were evacuated, with Dutch Prime Minister Mark Rutte convening crisis talks.
Flags flew at half mast across the Netherlands on March 19 as a tribute to the victims, and many people came to lay flowers at the site of the attack in Utrecht’s 24 Oktoberplein.