A University of Canterbury criminologist says it is very unusual for child sex offenders to abduct their victims.
Yesterday afternoon an 11-year-old boy was subjected to a four-hour ordeal after being taken from a West Auckland train station.
A man in a grey van asked the boy for directions before driving him to an unknown location and sexually assaulting him, police said.
Canterbury University professor in sociology and criminology researcher Greg Newbold said the fact the boy was abducted was very uncommon.
"Normally sex abusers groom kids and work on them slowly. Abducting someone is really unusual," he said.
"Normally when kids are abused it's by someone they know well, a relative or a friend or someone who has groomed them for a while."
Newbold said he could not think of any cases where a young boy was snatched and sexually assaulted during his time as a criminologist.
He said often when children were abducted they were also killed, citing the decades-long cold case of Tracey Ann Patient, who was abducted, sexually assaulted and murdered in West Auckland in January 1976.
"Someone who does this - you're dealing with a very dangerous sexual deviant," Newbold said.
Police have said they hope to have a better description of the offender after they interview the boy, who is recovering at home with his family after his abductor dropped him back in Ranui around 8pm.
"Police and Victim Support are doing everything we can to support them," said Detective Senior Sergeant Jason McIntosh.
"The victim has undergone a medical examination and specialist child interviewers are expected to speak with him today."
McIntosh said after that they hoped to have more details about the circumstances and a description of the offender.
"This is a very sensitive process though and at this stage we have limited information about the offender - he has been described as driving a grey van, was by himself, and had stopped the boy to ask for directions," said McIntosh.
"We are treating this as a priority investigation and CIB detectives, as well as detectives from the Child Protection Team, are working on this investigation."
Police said extra patrols were now in the area and appealed urgently for information about the grey van.
McIntosh asked anyone with information to contact him on 021 191 2659.
Information could also be given anonymously to Crimestoppers on 0800 555 111.