The two suspects, aged 30 and 40, were intercepted at Hong Kong International Airport’s departure restricted area on Wednesday evening as they prepared to board separate flights to the U.S. and Australia, The Standard newspaper reported.

The incident was discovered around 2 p.m. when staff at the Chai Wan MTR depot found two graffiti pieces, each measuring about 1 by 5 meters, sprayed on the side of a stabled train carriage, the South China Morning Post reported.

Staff then spotted two suspicious men wearing high-visibility reflective vests near the train.

The men fled toward the nearby Heng Fa Chuen residential estate after noticing the workers, scaling a three-meter-high perimeter wall.

Officers examining the site found that sections of anti-intrusion wiring along the top of the wall had been deliberately cut.

Police also seized nine cans of spray paint, a wooden ladder and two high-visibility vests.

Authorities launched an investigation, using public surveillance cameras and the Smartview system to track the suspects’ movements.

Police detained the duo before their flights left, and seized clothing allegedly worn during the crime from their checked luggage.

They are being detained on suspicion of criminal damage.

Police warned residents and visitors that criminal damage is a serious offense, carrying a maximum sentence of 10 years in prison upon conviction.

Hong Kong, the world’s second most visited city after Bangkok, welcomed 31.22 million visitors in the first seven months of the year, a 12% increase from the same period last year.