In images secretly shot by crime reporter Peter R. de Vries, Mr Van der Sloot is shown accepting a one thousand euros advance payment for his services. Independent lawyer J.P. Plasman says that by receiving the money Mr Van der Sloot has committed a punishable offence.
Judicial authorities in Thailand have requested copies of the images broadcast on Sunday by Dutch commercial tv channel SBS6.
Natalee Holloway disappeared in May 2005 while on holiday on the Netherlands Antilles island of Aruba, after spending a drunken night on the beach with Dutchman Van der Sloot. Her body was never found.
On earlier hidden camera footage, also produced by Peter R. de Vries, Mr Van der Sloot admitted that he knew how Ms Holloway disappeared. But lacking conclusive evidence, judges concluded it was impossible to declare Mr Van der Sloot guilty.
Mr De Vries has produced a new witness in the Holloway case. Press reports say that Mr Van der Sloot told a girlfriend, identified only as Celes, "Who knows, you may now be on the beach with someone who is able to get rid of a corpse."
According to judicial psychologist Harald Merkelbach, who watched both the earlier and the recent footage, Joran van der Sloot believes he is invulnerable. "He sees people as objects." The psychologist calls Mr Van der Sloot "a young man with many defects".
Following the latest disclosures about his behaviour, Mr Van der Sloot, using the alias of "Murphy Jenkins", is reported to have fled to avoid arrest by the Thai authorities. He has not been seen since leaving a party in Bangkok on Friday evening. A Dutch eyewitness claims he has seen Mr Van der Sloot on an internal flight to the island of Koh Samui.
Antillean film maker Renée Gielen has produced a tv documentary about the Natalee Holloway case. She says that unlike Peter R. de Vries she does not want to tackle Joran van der Sloot. "I'd rather focus on aspects that others have ignored."
Speaking in Oranjestad, Aruba, Ms Gielen accuses the Dutch press of blindly following the lead of US journalists after Ms Holloway's disappearance. "Nobody really investigated the Holloway family. Nobody published anything about a special medical flight from the US to Aruba, immediately after Natalee went missing. Neither the plane crew, nor local authorities were informed about the flight."
The documentary, entitled The Unrevealed Timelines, will be shown on tv channels on the Netherlands Antilles and will be released on DVD.