More must be done to strengthen security at Singapore’s key installations, said observers.

Commenting on the recent case of vandalism at the Bishan SMRT depot, they said the incident may have wider security implications.

On May 5, a train at the depot was apparently spray-painted with graffiti. This is the third time vandals have struck a key transport facility in four years.

It is believed a red scrawl with traces of white — measuring three metres long and one metre high — was found on a train’s middle carriage.

… Dr Kumar Ramakrishna, head of the Centre for Excellence for National Security at S. Rajaratnam School of International Studies, said: “This is hypothetical, of course. If they find out who is responsible is indeed from within, then certainly that calls for more stringent background checks.

“One of the potential scenario one could think of from a homeland security point of view, for example, one of cases we’ve had in Singapore — in the past a few cases actually — of self-radicalised individuals, these cannot be entirely ruled out.

“It always pays to be prudent. This is just a case of vandalism, but in future who knows, it may not be a case of vandalism, it might be worse.”