Police officer Iskandar Rahmat, 34, who has been arrested for the Kovan murders, crossed from Singapore to Malaysia on a scooter.

The senior staff sergeant from Bedok Police Division was in debt, had personal domestic problems, and was facing an internal disciplinary process, a press conference said. He has been in the police force for 14 years.

He crossed the border shortly after 11pm on Wednesday, the day the killings took place, and was arrested at a Danga Bay restaurant in Johor late on Friday night. He was taken in a car to the Police Cantonment Complex around noon on Saturday.

Police Commissioner Ng Joo Hee, speaking at the conference, said it was a sad day for the police. He said he regrets the actions of the suspect and wished he could "turn back the clock" to erase the hurt of the victims' family.

Deputy Prime Minister and Home Affairs Minister Teo Chee Hean said the suspect's actions have tarnished the reputation of the police.

It is unclear how Iskandar is related to the victims.

Car workshop owner Tan Boon Sin, 67, was killed in his 14J Hillside Drive terrace house in Upper Serangoon on Wednesday afternoon.

His older son, Mr Tan Chee Heong, 42, was seen staggering out of the house before collapsing in a pool of blood at about 3.40pm.

A few minutes later, someone drove the elder Mr Tan's Toyota Camry out of the house, in the process running over the younger Mr Tan.

The body was dragged by the car for more than 1km before it was dislodged outside Kovan MRT station. The driver sped off.

Officers who went to the Kovan MRT station site discovered a trail of blood. It led all the back to the Hillside Drive house, where the father's body was discovered.

The abandoned car was found on Thursday morning in a quiet part of Eunos industrial estate.