Dutch police were investigating terror ties in the Utrecht gun attack that killed three people after discovering a note in the getaway car that pointed to extremist links.
Prosecutors said Gokmen Tanis, the 37-year-old suspect who was seized after an armed stand-off, is being held on suspicion of manslaughter with a possible terrorist motive.
It is not immediately clear as to what the note said and the authorities are leaving open the possibility that the alleged killer was acting out of personal grievances. He had appeared in court days earlier to answer a charge of alleged rape.
Nine people suffered wounds and three people died from the shooting in the university city.
The victims were identified as a 19-year-old woman and two men, aged 28 and 49, and all were from Utrecht.
Tanis, believed to be of Turkish descent, was arrested alongside two other suspects on Monday following a manhunt by anti-terror police and armed units surrounding an apartment close the vicinity of the shooting.
Both Dutch and Turkish media have speculated that the shooting could be linked to a break down of a relationship, citing interviews with neighbours of the suspect.
An uncle of Tanis who lives in the Netherlands dismissed claims of potential motives linked to radicalisation. He told Turkey's state-run Anadolu news agency that the suspect was at a low ebb in life.
“Looking at my nephew's condition, the possibility that what he did was a terror attack is low,” said Mahmut Tanis in an interview with Turkey’s state-run Anadolu news agency.
He added that he had not seen him in years and that his actions could stem from “matters of the heart”.
“The investigation has so far revealed no relationship between the main suspect and the victims,” a police statement said.
In addition previously appearing in court accused of rape, Tanis was reportedly known to police including violent threats made to a woman.
While he is not known for extremism, Dutch newspaper Algemeen Dagblad reported Tanis’ brother is connected to a Turkish radical Islamic and anti-democratic splinter group. Whether any connection between his brother's ideas and the attack has not been made so far.
A 47-year-old woman also told the Dutch newspaper that Tanis was a drug user with a criminal record and he is facing trial for raping her in 2017.