A man places a heart-shaped balloon next to flowers at the site of a shooting in Utrecht, Netherlands. (Piroschka Van De Wouw/Reuters)

Dutch investigators said Tuesday that terrorism was “a serious possibility” in a shooting that killed three people on a tram a day earlier in Utrecht, citing a note found in the suspect’s vehicle that they said gave new guidance about the potential motive for the attack.

The Monday morning violence unsettled the Netherlands, which has largely been spared the type of terrorist attacks that have struck neighboring countries, including Belgium. Counterterrorism officials had been especially on guard after a shooting Friday in New Zealand that killed 50 worshipers at two mosques.

But in the chaotic hours following the attack in Utrecht, investigators struggled to piece together a motive. By the end of Monday, Dutch news outlets were flooded with accounts — incorrect ones, prosecutors suggested Tuesday — that said the 37-year-old Turkish-born suspect had targeted a woman on the tram over a family dispute.

“The investigation has so far shown no relationship between the main suspect and the victims,” Dutch prosecutors said Tuesday in a statement. “So far, a terrorist motivation is being taken as a serious possibility. There is cause for this because of, among other things, a letter found in the getaway car.”

They offered no details about the contents of the letter and said they were not excluding other possible motives.

A Dutch court said Tuesday that Gokmen Tanis, the suspect, also faces rape charges over a July 2017 incident and that he had been sentenced this month for burglary and shoplifting. In 2014, he was convicted of illegal weapons possession and attempted theft, and acquitted of attempted manslaughter. Courts had allowed him to remain free despite the burglary and shoplifting convictions because he had not exhausted his appeals. He was on pretrial release in the rape case.

Tanis was caught by police Monday evening after an intense manhunt that put much of Utrecht on lockdown. He had a firearm when he was arrested, prosecutors said. Amid contradictory information from authorities, fearful residents Monday had little sense of whether there was a risk of further attacks.

Police also arrested two other men, a 23-year-old and a 27-year-old, both Utrecht residents, and were trying to determine whether they had any role in the attack, the prosecutors said.

The three victims were a 19-year-old woman from Vianen, a town close to Utrecht, and two Utrecht men ages 49 and 28, the prosecutors said. Five people were injured, three of them critically.

Mourners piled flowers at the base of a tree at 24 Oktoberplein, a busy intersection in southwestern Utrecht that was the site of the attack. Dutch flags flew at half-staff on government buildings.

The attack has stunned the Netherlands, where citizens will vote Wednesday in regional elections that could shake up the ruling coalition. An anti-immigration party has been surging in opinion polls, and party leaders capitalized on Monday’s attack to hit Prime Minister Mark Rutte for what they said was an overly open immigration policy.