BERLIN — Prosecutors said Thursday that the tram shooting this week in the Dutch city of Utrecht that left three people dead and five wounded may have been a terrorist attack. The 37-year-old Turkish-born suspect, Gokmen Tanis, is being investigated over several offenses, including manslaughter or murder “with a terrorist motive.” He will face a judge on Friday.

In a statement Thursday, the Netherlands’ Public Prosecution Service said “no relationship between the suspect and the victims has yet been found.” Investigators usually seek to establish whether attackers have personal connections to their victims to rule out other motivations, such as family disputes or revenge crimes.

While no evidence has been found so far that accomplices may have helped in planning and executing Monday’s attack, investigators cautioned that the suspect’s radicalization may not fully explain the shooting and that “personal problems” may have played a role.

Many recent attackers who appear to have justified their actions by referring to extremist ideology also had a history of mental illness. Investigators in Europe have struggled to clearly distinguish between acts committed by mentally distressed individuals and ideologically motivated crimes. 

Dutch authorities said Thursday that the 37-year-old suspect would undergo a psychological examination.

Monday’s shooting came four days after at least 50 people were killed in a right-wing extremist attack on two mosques in the New Zealand city of Christchurch.