Four vandals have been captured on video tagging an Auckland Transport train while filming the attack themselves on GoPro cameras.
A passenger aboard the train noticed the four people outside her window at Swanson at 8.20pm on Sunday night.
She began filming on her cellphone as the group, with faces covered up, tagged the side of the train in green paint, while apparently making their own recording of the act.
Auckland Transport (AT) was aware of the incident and provided its own CCTV footage to police.
"The train was taken out of service and washed overnight at our facility in Wiri and was clean and back in service yesterday morning," AT spokesperson Mark Hannan said.
Auckland's trains were treated with a film so tags can be easily washed off.
The cost of vandalism and other damage to the trains was around $500,000 per year.
"This vandalism is a cost to ratepayers and we do pursue cases through the courts," he said.
"These idiots are wasting everyone's time and money."
Tagging is typically subject to a charge of wilful damage, which carries a maximum sentence of three months imprisonment and/or a fine of $2000.
A police spokesperson confirmed police were investigating.
People with information that could assist police were asked to contact the Henderson Police Station on (09) 839 0600.