GEORGE TOWN • A bodyguard who allegedly shot dead his boss and two others on an expressway in Penang has a history of mental instability, reported Malaysian media.

"Our initial investigations show that the gunman has a mental problem. He also had previous military training as an army reservist and has a valid firearms licence," the New Straits Times quoted Inspector-General of Police Khalid Abu Bakar as saying at a press conference yesterday.

The man had no previous criminal record, added Tan Sri Khalid. Police declined to identify the man.

The suspect, who is in his 40s and who worked for businessman Ong Teik Kwang, 32, was arrested at the scene soon after the incident at 7.30pm on Thursday.

A second suspect, Mr Ong's driver who is also in his 40s, was arrested a few hours later, the newspaper said.

Both suspects have been remanded for seven days to assist in investigations.

The report, citing state police chief Abdul Ghafar Rajab, said the incident was triggered when Mr Ong discovered that his driver was intoxicated and unable to drive.

He decided to take over from the driver while they were travelling on Tun Dr Lim Chong Eu Expressway.

But this led to an argument with the bodyguard, who pulled out his gun and opened fire.

He aimed at Mr Ong, killing him, and then continued to shoot randomly, according to the report.

The subsequent shots killed or injured nearby motorists, the report said. The two others killed were Mr Senthil Murugiah, 38, and Mr Choi Hon Ming, 32.

Five people were injured, including a videographer from Radio Television Malaysia, Mr Amirul Amin Mohamed Amer. He was hit in his shoulder by a stray bullet while riding his motorcycle along the expressway. The 28-year-old is reported to be in a stable condition.

The suspect surrendered to the police after the rampage, Penang district police chief Mior Faridalathrash Wahid was quoted as saying by Agence France-Presse.

"Police approached the shooter and ordered him to surrender. He obeyed police instructions and we arrested him," he said.

The incident brought traffic to a standstill for six hours.

According to a witness who lodged a police report on Thursday, she was driving along the expressway when she noticed a man bleeding from the head and face.

Thinking that a traffic accident had taken place, she stopped and offered to take him to hospital, reported The Star.

On their way to hospital, the man asked her if he could use her phone to contact his family, she said in her report.

She then overheard the injured man saying that "the bodyguard had gone mad" and that "tailo (boss in Cantonese)" was dead.