Seeing a man brush his hand against a woman's buttocks at Yishun MRT station on Oct 23, Mr Jay Liu, 29, followed him.

Thinking he was about to apprehend a molester, Mr Liu was shocked when the man molested two more women in five minutes.

With the help of a passer-by, the off-duty Cisco officer stopped the suspected serial molester.

Yesterday, both men were among six people who were presented with the Public Spiritedness Award at the Public Transport Security Command yesterday for stopping four sex predators at four MRT stations recently.

At the awards ceremony yesterday, Mr Liu told the media he followed the suspect, who was in his 30s, after the man touched the first victim. Seconds later, he saw him trying to brush his arm across another woman's chest but he missed and hit her arm instead.

Mr Liu followed the man down on an escalator and saw him touch the buttocks of a third woman. Mr Liu immediately approached the woman, who confirmed she had been touched.

He confronted the man, bringing him to a quiet spot next to the escalator, and questioned him.

Mr Liu said: "He was on a spree. He said it was a mistake, and then denied his actions, trying to get away. But I forced him into a squatting position by pressing his shoulders down."

Another commuter, Mr Edwin Khoo, 37, an events planner who did his National Service with the police, said he heard the commotion and helped Mr Liu detain the suspect.

Mr Khoo said: "I was thinking a brother in blue needed help, and the suspect was quite big-sized. Thankfully, the police came within five minutes."

The suspect was arrested for outrage of modesty at about 7.10pm.

On the same day at about 8.30am, a man in his 60s was caught after allegedly taking upskirt photos of a young woman, who was sitting opposite him, on a train at Sembawang MRT station.

Unfortunately for him, he was sitting between Mr Eric Tan, 23, an off-duty Aetos officer, and Mr Lum Hui, 27, a financial analyst and volunteer special constabulary officer.

The two men, who did not know each other, noticed what the suspect had done and quickly grabbed his phone to prevent him from deleting the photos. The police arrested the man.

Mr Tan and Mr Lum were also presented with the award yesterday.

The two others commended were Mr Colin Toh, 24, a student, and Mr Thng Kay Beng, 35, an accountant, who helped catch suspects in two other upskirting cases at Serangoon and Yio Chu Kang MRT stations respectively.