Security measures for dozens of people involved in the investigation into gangster Ridouan Taghi have been beefed up security since the murder of lawyer Derk Wiersum last week, broadcaster NOS said on Tuesday.

Some have given camera surveillance, others round-the-clock services by the same elite team as protects the royal family, NOS said.

Wiersum, who represented a key crown witness in the case, was shot dead outside his home in Amsterdam six days ago.

Pre-trial hearings will continue at the high security courthouse at Schiphol airport on Tuesday, during which judges will discuss how to proceed following the murder, NOS said.