SINGAPORE - The three men assisting the police with investigations over the white substance left at Woodleigh MRT Station on Tuesday (April 18) are joggers from a running group, The Straits Times has learnt.

ST understands that the trio were helping to mark a trail before the main run took place.

A 69-year-old man was arrested for an offence of public nuisance on Tuesday. Hours later, the police said two other men - aged 53 and 70 - were also assisting in investigations.

ST understands that all three are locals and that they are part of a running group: Seletar Hash House Harriers.

According to its website, Seletar Hash House Harriers was established in 1980.

The website lists a run on Tuesday (April 18) at 5.30pm from Block 150, Serangoon North Avenue 2.

In its description, the Seletar Hash House Harriers wrote that they are a "running/drinking/social club which was started by bored expatriates in Kuala Lumpur, Malaysia, in 1938".

It went on to explain that hashing is where runners set a course in advance of other runners by marking out a trail with white flour, toilet paper and or chalk marks.

Hashing has been done in other countries such as the United States.

In 2007, two people who sprinkled flour in a parking lot for their "hash" run sparked a bioterrorism scare, NBC News reported.

A cleaner had found the flour sprinkled at various parts of the station, MP Melvin Yong, who is also executive secretary of the National Transport Workers' Union (NTWU), said in a Facebook post on Tuesday.

The station was closed for about three hours and the Singapore Civil Defence Force dispatched HazMat officers to the scene.

The incident comes more than two weeks after Hougang MRT Station was briefly shut down due to security concerns over an unattended bag.

A 39-year-old man was arrested in that instance, which occurred on April 2.