As a teenager, he, along with his classmate Cor van Hout, was part of a gang that worked for landlords in evicting squatters, and may have been involved in several robberies.

After Freddy Heineken's release, the kidnappers—Cor van Hout, Willem Holleeder, Jan Boellaard, Frans Meijer, and Martin Erkamps—were all eventually traced and served prison sentences.

Several million guilders of the Heineken ransom were never traced, and may have been part of the initial sum he and Cor van Hout hoped to use for a new extortion empire; there are said to have been up to 24 people in his crime ring.

[citation needed][9][10][11] After his release from prison in 1990, Holleeder was close to Willem van Boxtel, the president of the Hells Angels Amsterdam chapter.

[2] It is suspected that Holleeder, along with his partner-in-crime Dino Soerel, ordered the murder of both Willem Endstra and John Mieremet,[15] who was shot and killed in Thailand on 2 November 2005.

Holleeder's name keeps turning up in this connection although three suspects in the Endstra murder, Ali N. and C. Özgür of Alkmaar and Cleon D. from Almere have been released.

The Dutch newspaper De Telegraaf reported on 16 July 2006 that Holleeder and Cor van Hout had planned to kidnap Prince Bernhard instead of Freddy Heineken in the 1980s.

Thomas van der Bijl, who was murdered in his bar in Amsterdam in April 2006, made these allegations in a deposition before the Dutch national police.

[citation needed] His lawyer, Bram Moszkowicz, argued that media depictions of Holleeder as one of the "topcriminelen" had prejudiced the case against him.

[8][29] In April 2016, Holleeder was arrested again, while still in prison, for allegedly soliciting two members of a gang (known as the Curaçao No Limit Soldiers) to kill his sisters Astrid and Sonja as well as Investigative Journalist Peter R. de Vries, a witness in the mega-trial.

[10] In July 2019, the Court in Amsterdam convicted Holleeder after a lengthy and extensive trial[30][31] at the age of 61 to life imprisonment for his involvement in a series of five murders, including that of his former friend and criminal associate Cor van Hout, and one case of manslaughter,[32] thus following the demand of the prosecutor[33][34] and brushing off his denials.

[36][37][38] The judges also found that he had formed a crime gang and ordered killings with jailed associate Dino Soerel and since-murdered criminal Stanley Hillis.