One of Holland's biggest murder trials started on Monday, with Ridouan Taghi facing multiple charges of murder and of running a hit squad.
Sixteen other suspects are also on trial.
Tight security was in place at the Amsterdam courthouse known as "The Bunker", with two helicopters and a fleet of armoured vehicles surrounding the building.
He is accused of ordering six murders between 2015 and 2017 as part of a Moroccan drugs war, and of being the mastermind behind the hit squad known as the "Angels of Death".
Mr Taghi, 43, is also accused of attempting to blow up a car belonging to Dutch criminal Martin Kok in 2016, using a bomb that had the power of 40 hand grenades.
The Moroccan-Dutch national was hiding out in Dubai with his wife and six children until he returned to the Netherlands for the trial.
The 17 people on trial are charged with planning a total of 13 gangland murders, of which six were carried out.
Through his lawyer, Mr Taghi said he had nothing to say.
The prosecution claims the accused were all "an indispensable link in an organisation that aimed to commit murders".
Said Razzouki, who is accused of being Mr Taghi’s second in command, was arrested in Colombia in February last year and is awaiting extradition. He is being tried in absentia.
Outside court, a protest was held by campaigners, many wearing T-shirts with the slogan "Free T", claiming the trial is unfair and demanding the release of Mr Taghi.
The case generated intense security after lawyer Derk Wiersum, who was representing the prosecution's key witness – known as Nabil B, was murdered.
Nabil B's brother was also murdered.
On Monday, the court heard Nabil B had been arrested for possessing a weapon in 2017.
After discussions with investigators he agreed to give evidence linking Mr Taghi and others to a number of murders in return for receiving a lower prison term of 12 years.
The witness told the court his decision was due to the "[drugs] war getting terribly close" and revealed an attempt had been made to kidnap Mr Taghi's alleged right-hand man, Mr Razzouki.
"I found out that Ridouan wanted to kill me,” Nabil said.
He told the court the statements he has made are “the absolute” truth.
The trial, which was brought after more than 100 detectives were involved in a three-year international investigation, is expected to last at least a year.