Officials in Utrecht should have been clearer in their communications about the shooting on a tram in the city six months ago, according to an official report into the way the city and emergency services dealt with the incident.

The police advice to people to stay indoors was correct, but communication about the need to remain inside and the length of time could have been better, the report by crisis management institute COT said.

In addition, communication between the emergency services was difficult, making it harder for them to get an overall picture of what was happening. And police were too quick to talk about an ‘attack with a terrorist motive’, the report said.

Utrecht’s mayor Jan van Zanen commissioned the report to assess how communications could be improved in future incidents.

Utrecht was brought to a complete standstill on March 18 at 10.45am when the first reports of a shooting on a tram were issued. Residents were ordered to stay inside for several hours while heavily armed police hunted the gunman, leading to deserted streets. The lock-down was not lifted until the afternoon.

In total, four people were killed and several others injured when a man opened fire on a busy tram.

Main suspect Gökmen Tanis, 37, was arrested in the evening of the attack. He is due to appear in court again next Monday for a procedural hearing.