Lawyers and prosecutors in major gangland drugs cases in the Netherlands have been given emergency protection after the unprecedented murder of a top defence lawyer prompted police and the media to claim that government naivety was turning the country into a narco-state.

Derk Wiersum was gunned down in the street as he left his home in the Amsterdam suburb of Buitenveldert on Wednesday morning. Police are searching for a 16- to 20-year old man in a black hooded top who fled the scene on foot.

Wiersum, 44, was acting for Nabil Bakkali, a crown witness in a case against 16 men accused of five murders between 2015 and 2017, whose brother was also shot dead last year shortly after authorities named Bakkali as a witness.

Dutch media compared Wiersum’s killing to the targeted Mafia assassinations of investigating magistrates in Italy in the 1990s or the lawless Colombia under the drugs baron Pablo Escobar.

A woman lays flowers near the home of the murdered lawyer Derk Wiersum in Amsterdam on Thursday. Photograph: Robin Utrecht/EPA

Flags were at half-mast outside courtrooms across the Netherlands on Thursday and lawyers were to hold a minute’s silence as the justice minister, Ferd Grapperhaus, met officials from the public prosecutors’ office and representatives of Dutch lawyers’ associations to discuss the heightened security arrangements.

The chief public prosecutor, Fred Westerbeke, told Dutch TV that while measures had been taken to protect lawyers and officials in the case, the possibility of murder had not been considered. “We are obviously taking more steps now,” he said.

Grapperhaus described the killing as a “disgusting attack … on our rule of law”, adding that the “safety of people who work to guard that must be beyond question”. Calling for a new approach to organised crime, the national police chief, Erik Akerboom, said Dutch society “cannot accept this. A line has been crossed.”

The mayor of Amsterdam, Femke Halsema, described the murder as “a shock for our society, because the victim was doing his job and it’s a very important job in our constitutional state”, while the prime minister, Mark Rutte, called the shooting “extremely disturbing”.

The Dutch counter-terrorism agency, NCTV, has been put in charge of the investigation into Wiersum’s murder.

Concern has been growing over increased violent crime levels in Amsterdam, where recreational drug use has long been tolerated, creating a flourishing underworld of dealers and suppliers. A leading police union said the situation was out of control.

Amsterdam’s red-light district at night. Photograph: Koen van Weel/AFP/Getty Images

“This is confirmation that we live in a narco-state,” said Jan Struijs of the NPB union, which last year warned that the government and politicians were underestimating the scale of organised crime in the country.

A report last month for Amsterdam council said the city’s relaxed drugs policies had “given free rein” to “drugs criminals, hustlers, parasites, middlemen and extortionists”, adding: “Drug-related organised crime – the ‘underworld’ – now exerts a significant influence on our city.”

Two of the main suspects in the case Wiersum was working on, Ridouan Taghi and Said Razzouki, are on the Netherlands’ most wanted list and the subjects of international arrest warrants. Eleven men, all alleged members of a cocaine-smuggling gang, are in custody, including Bakkali, who has provided police with more than 1,500 pages of statements against the group in exchange for a more lenient sentence.

The AD newspaper said the murder marked the beginning of a “new, dark phase” for the country, adding that although in the Netherlands “the prime minister still cycles to work” and lawyers, judges and prosecutors “move unguarded through life … the underworld has just strengthened its hold on the upper world”.

The paper said that despite plenty of government money and declarations of good intent, authorities “do not yet have a grip on the threat”, leaving police and justice officials “at the mercy of a narco-state over which the government has no control”.

The NRC Handelsblad newspaper said the Netherlands was “naive” in its approach to drugs, citing EU policing officials and unnamed sources in the drugs world, particularly Colombia, who allege the country is “the logistical centre for the cocaine trade in western Europe”.

The paper said that based on the 70,000kg cocaine seized in the ports of Antwerp and Rotterdam in 2018, at least 200,000kg must have been brought successfully into the Netherlands, worth an estimated €5bn (£4.4bn).

NRC said it was doubtful whether authorities had yet fully grasped the extent of the impact of such sums on Dutch society. “Put simply,” the paper said, “that kind of money buys anything – cars and nice houses, but also contract killers and corrupt officials.”.

John van den Heuvel, a crime correspondent who has been given police protection when reporting on Dutch gangs, told state radio he was “extremely concerned, again, at the way in which organised crime is underestimated in the Netherlands. Of everything I’ve experienced, this is an absolute low.”