The Dutch police said on Tuesday that they were still considering terrorism as a motive for a deadly shooting on a tram in the city of Utrecht based partly on a note they discovered.
The shooting on Monday, which left at least three people dead and five injured, and an ensuing manhunt prompted heightened security and sent ripples of fear through the Netherlands. A 37-year-old immigrant from Turkey was arrested Monday night.
People who know the suspect, Gokmen Tanis, and family members in Turkey quoted by news organizations there, had said on Monday that they believed the assault was some kind of domestic dispute.
But the police said they had so far found no links between Mr. Tanis and the three people killed on the tram.
“Thus far, a terrorist motive is being strongly considered,” the national police said on Tuesday.
“The reason for this, among other things, is a note found in the getaway car,” they said, but did not elaborate. “Other motives aren’t being ruled out, these are being investigated as well.”
The shooting jarred a country where gun violence is rare, and which has not seen the kinds of major terrorist attacks that have rocked Belgium, Britain, France and Germany in recent years. It came just days after a gunman, thought to be a white nationalist, killed 50 people at two mosques in Christchurch, New Zealand, prompting fears of either copycat attacks against Muslims or retaliatory attacks by them.
The police said on Tuesday that they had found a firearm when Mr. Tanis was arrested. They did not say what kind of gun it was, or whether it was the weapon used in the attack.
Mr. Tanis had been arrested several times before and was facing a rape charge. People who knew him from the Kanaleneiland neighborhood of Utrecht, home to many immigrants from Turkey and Morocco, described him as erratic, troubled and aggressive.
The Utrecht shooting took place around 10:30 a.m. near 24 October Square, and the gunman or gunmen — there were conflicting accounts about the number of assailants — fled. The police said the theft of a car at gunpoint nearby was tied to the attack, but the details were unclear.
Three people — a 19-year-old woman and two men, ages 28 and 49 — were killed in the attack, and five others were injured, three of them seriously. Officials have not publicly identified any of the victims.
Unsure of the motive, how many people were involved, or where the killer was, the authorities quickly ramped up security and raised the terrorist threat assessment in Utrecht Province to the highest level. For several hours, the tram service was shut down around Utrecht, people were told to remain indoors, schools were locked down and officers in body armor were deployed to police stations, airports and other key locations.
In addition to Mr. Tanis, two men in their 20s were arrested on Monday in connection with the shooting, but the police acknowledged that it was not clear what role, if any, they may have played in it. They said on Tuesday that the men, whom they did not identify, were still in custody and were being questioned.