A northbound SMRT train which was found vandalised on Wednesday morning was pulled out of service.
Transport operator SMRT released a statement saying that a train officer had discovered graffiti on the train. Initial investigations revealed a breach in the fence at Bishan Depot where the train was parked.
It added that the breach took place at a location where upgrading works to the security measures were being scheduled, reported The Straits Times.
"We are very concerned that despite stepped-up patrolling of the perimeter of our depots, this incident took place," it said in the statement.
Meanwhile, the Land Transport Authority (LTA) has expressed its disappointment over SMRT's failure to prevent another security breach at its depot.
"LTA therefore takes a very serious view of this second security breach and will not hesitate to take SMRT to task if investigations show that SMRT did not comply with the necessary security standards at its depots."
This is the second incident in two years that an SMRT train has been vandalised. Last May, two vandals managed to cut through the fence at SMRT's Changi Depot and spray-painted graffiti on one side of a train.
Swiss national Oliver Fricker, a 32-year-old software consultant, was jailed seven months and given three strokes of the cane for trespassing and vandalising. He has since been released from prison.
His alleged accomplice, 29-year-old Briton, Lloyd Dane Alexander, remains at large.
The LTA also pointed out that a recent review -- conducted after last year's incident -- by the Public Transport Security Committee (PTSC) had instituted a whole range of more stringent security standards to strengthen security in all train depots which SMRT has accepted.
In its statement, the police said that it will not tolerate such acts which blatantly disregard the law. It added that investigations are ongoing while SMRT is said to be conducting its own internal investigations.
Anyone convicted of vandalism could be jailed up to three years, or fined up to S$2,000 and given between three and eight strokes of the cane.
The penalty for trespassing into a protected place is a jail term of up to two years, or a S$1,000 fine, or both.