At the time of his death, Wiersum was a lawyer for state witness Nabil B. in the Marengo case against the so-called 'Mocro Maffia' led by Ridouan Taghi.

[1][2][3] Derk Wiersum started as lawyer of Nabil B. in the Marengo process against the Mocro Maffia allegedly led by Ridouan Taghi in 2017.

Ridouan Taghi and his henchman Saïd Razzouki were being prosecuted for ordering these murders and for leading a criminal organization.

[5][6][7][8][9] In the morning on 18 September 2019 around 7:40 a.m. local time, Derk Wiersum left his home in the Imstenrade in the Amsterdam neighborhood Buitenveldert to go to his work by car.

Besides his work as lawyer and judge, he was treasurer for Stichting Rechtshulp Terdoodveroordeelden, a now defunct anti-death penalty organisation that provided international legal assistance to convicts who had been sentenced to death, and he worked as a lawyer for the Dutch & Detained foundation, which provides independent legal advice to Dutch nationals who are detained abroad.

Anouar Taghi was a member of the Utrecht 'Audi-bende', a gang that robbed ATMs using explosives (a so-called plofkraak), driving away in fast cars with a preference for the brand Audi.

The criminal investigation department assumes that he led a group of co-suspects who were dealing with stolen cars, used for ram-raiding and plofkraken.

Those cars were parked in a warehouse in Utrecht, cleaned and "whipped" (checked for eavesdropping equipment or monitoring beacons).

[11] At the end of April 2020, Anouar Taghi was arrested for his involvement in an attempted murder and for participation in a criminal organization.

Sources within the criminal circuit state that the victim of the sledgehammer attack also belonged to the organization, but no longer wanted to cooperate.

[24] On 6 January 2020, the OM announced that the man arrested in October is the 36-year-old Giërmo Brown from Almere, he is of Surinamese descent.

[25][26] When the getaway car, white Opel Combo, was shown on television by the police, Brown bought a plane ticket to Suriname.

[31] Giërmo Brown and Moreno Bieseswar flew together from Paris to Suriname through French Guiana on 28 March 2019.

Both men are suspects in the murders of the 49-years-old Dennis Groenfelt from Utrecht and the 19-years-old Surinamese girl Cadischa Prika in Paramaribo on 6 May 2019.

[21][34][35][22] 23-year-old Jerlonny P., also known as rapper Kerron, from Brunssum was arrested for stealing the Volkswagen Transporter and delivering it to Anouar Taghi.

F. was arrested in October 2021 in Morocco for his suspected involvement in the Café La Crème lounge shooting in Marrakech in 2017, in which a son of a prominent Moroccan judge was killed.

There are camera images, evidence Brown's debit card was used when refueling and the data from his phone matches the movements of the car on twelve dates.

The judiciary is convinced that the group around Anouar Taghi delivered cars to the perpetrators of the murder, such as the Renault Mégane and the Volkswagen Transporter that appear to have been used for pre-observations.

In Taghi's home the police found equipment for tracking cars and jammers, for disrupting means of communication: things that are frequently used in the harsh criminal environment, including during liquidations.

[11] The Renault Mégane, who drove at least 26 times through the street where Wiersum lived in August, was signaled during a police operation in Taghi's warehouse in Utrecht in the same month.

The judiciary says Anouar Taghi ordered a few days after the murder to set the Renault Mégane on fire, the car was found burned out in Voorburg.

On 16 and 17 September, Wiersum left by bicycle instead of by car, after which the Volkswagen Transporter and the Opel Combo drove out of the street.

The criminal investigation department assumes that the perpetrators were surprised by Wiersum leaving home by bicycle, and therefore postponed the murder.

[13][41][42] On 29 July 2020, Anouar Taghi confessed that he hired warehouses under a false name to park stolen cars together with Oussama B. and Jesse S. from Utrecht.

[44][45] The fact that Brown and B. flew together to Suriname in March 2019 proves that they knew each other before the murder of Derk Wiersum.

[53] Since Wiersum's murder, a total of 20 to 30 people closely related to the Taghi case have received extra security.

The people who are the closed linked to the case receive personal security provided by the Royal and Diplomatic Protection Service (DKDB).

Grapperhaus said about the lawyers, public prosecutors and judges: 'They play an indispensable role in our rule of law.

'[61] In December 2020, the NCTV told lawyers Peter Schouten and Onno de Jong they are on a death list, because of their role in the Marengo process.

[62] On 6 July 2021, Peter R. de Vries, the confidential counselor and the spokesman of Bakkali and his family, was shot in the head.