There is one unsolved case that still bothers Steve Vickers.
In 1983, property tycoon Teddy Wang Teh-huei was kidnapped, but he managed to walk away unharmed, thanks to a ransom of US$11 million paid by his wife Nina Wang Kung Yu-sum.
But when he was kidnapped again, in 1990, his luck ran out. His wife paid six times more in ransom and the culprits were caught. But Wang was never seen again.
Vickers was then the head of the Royal Hong Kong Police Force's Criminal Intelligence Bureau (CIB).
He had a stellar record with kidnappings. Of the 28 cases he handled during his career, he brought back 26 victims alive - but not Wang.
The Englishman joined the Royal Hong Kong Police Force in 1975. His initial two-and-a-half-year contract turned into a lifelong commitment to the city.
As criminal intelligence chief, Vickers was responsible for negotiating with abductors. It was a stressful part of his job, but seeing kidnap victims returned safely made him happy.
Vickers says kidnapping cases are scarier than murder or fraud when the harm is already done.
"If you make a mistake in kidnapping cases, you can cause further damage," he notes.
"You have to be very careful how you conduct operations. That's why we have very sophisticated response surveillance."
But many criminals have become more sophisticated, too.
"Sometimes the victim is kidnapped in one city," Vickers explains. "But the calls demanding money are traced overseas and money transfers need to be made elsewhere still."
Often cases require close co-operation among police forces across the region. The key to success is patience, Vickers says.
Police need to follow leads and gather evidence carefully before moving in. Even then, it could take several months to solve a case.
Hong Kong was a wilder place back in the 1980s and 1990s, with waves of armed robberies. Guns - many of them smuggled in from the mainland - were used by many criminals.
Vickers says organised crime is "a cancer in our midst". Triads, he says, pose a great challenge for law enforcement. "But we dealt with the problems and now Hong Kong is a safe city," Vickers says. "The work done by the CIB was critical."
In 1992, he finally took off his uniform and joined the private sector as an investigator tackling white-collar crime.
His role changed. He was once a prosecutor who had the authority to issue search and arrest warrants. Now he is an expert who helps multinational companies check out the background of potential business partners. He also works on internal fraud cases and crisis management. And occasionally he needs to deal with cases of kidnapped executives.
Some clients seek Vickers' help on alleged fraud because they do not have enough evidence to make a credible complaint to the police.
"Our [my company and the police] actions are not mutually exclusive," Vickers says. "We are not competing with the police in any way. Our work complements the work of the police," he stresses.