Lawyers, the police and politicians have reacted with shock and horror at the ‘unprecedented’ murder of a top criminal lawyer, who was shot dead in Amsterdam on Wednesday morning.

Derk Wiersum was defending a crown witness in a major gangland investigation and there are suggestions there may be a connection with the case. The national terrorism agency NCTV has been drafted in to help with the investigation.

Wiersum was representing Nabil B, a key witness in the case against gangland boss Ridouan Taghi. Taghi is said to be behind a string of killings in Utrecht and Amsterdam in the ongoing the ongoing ‘mocro mafia’ drugs wars.

Last year Nabil B’s brother was also shot dead, in what is thought to have been either a warning to Nabil not to testify or a case of mistaken identity.

The shooting happened around 7.30am. Neighbours reported hearing several shots and the gunman, said to be aged 16 to 20 and dressed in black, made off on foot. According to some witnesses Wiersum was with his wife when he was killed.

Wiersum was a partner in a major Amsterdam law firm and focused on cases involving organised crime. He had previously warned that the public prosecution department is not doing enough to protect crown witnesses. He was also a part-time judge.

Flowers have been left by well-wishers at the door of the law firm where he worked.

Bloemen bij het advocatenkantoor van de overleden #advocaat #Derkwiersum in #Amsterdam. mensen uiten hun medeleven. De deken van de Amsterdamse #orde van Advocaten vertelde net dat dit een aanslag is op de rechtstatelijke orde van Nederland. pic.twitter.com/T3KabgTNs7 — Silvia Brens (@SilviaBrens) September 18, 2019

Prime minister Mark Rutte and legal affairs minister Sander Dekker said they are extremely shocked by the killing and Amsterdam mayor Femke Halsema has called an emergency meeting of police chiefs and justice ministry officials. ‘This case has the highest priority,’ the mayor said.

‘Details are still sketchy so we must be careful about drawing conclusions, but it is shocking that such a thing can happen in our democracy. We wish his family and colleagues much strength at this difficult time,’ the Dutch bar association said in a statement.

National police chief Erik Akerboom described the murder as brutal. ‘This brutal murder has broken new boundaries,’ he said. ‘Now people just doing their job would not appear to be safe.’