Nui was charged with the rape and murder of six-year-old Nong Cartoon last month.
Crime Suppression Division commander Pol Maj Gen Supisal Pakdeenaruenart, who is working on the case, said he had written to the FBI legal attaché office at the United States embassy in Bangkok asking it to send specialists in the field of serial killer behaviour and crime scene investigation to assist the probe.
Nui, also known as Ting Tang, 32, confessed that he had kidnapped and raped nine other young children, four of whom he allegedly killed, after he was arrested for raping and killing Nong Cartoon near Bearing BTS skytrain station on Dec 6 in Bangkok's Bang Na district.
However, police are yet to confirm his claims and are still investigating exactly how many children may have been slain by the suspect.
Pol Maj Gen Supisal said earlier this week that investigators believe the behaviour of Nui matches that of a ''hedonistic serial killer'' who targets victims for personal pleasure.