Facing a flurry of questions from lawmakers in parliament over the decision – a subject of public debate in recent weeks – Minister Indranee Rajah said there was “a lack of sufficient evidence, either documentary or through witnesses, which would establish any criminal charge beyond a reasonable double against a specific individual”.

The decision was taken following exhaustive investigations by the country’s powerful Corrupt Practices Investigation Bureau (CPIB) and the Attorney-General’s Chambers, Indranee said.

The cross-border nature of the case and a lack of witnesses made prosecuting the six executives difficult, the minister in the prime minister’s office said.

Lawmakers’ questions on the matter follows a statement issued by the CPIB on January 12 stating that the six individuals – which the agency did not name – had been issued stern warnings in lieu of prosecution. The agency cited “evidentiary difficulties” in its probe.

The case made national headlines in 2017 when Keppel Offshore & Marine (Keppel O&M) – shipbuilder Keppel’s rig-building unit – agreed to pay around US$422 million in fines as part of a global resolution with criminal authorities in the US, Brazil and Singapore.

It was the largest corruption case involving a portfolio company of state investor Temasek Holdings. Sembcorp Marine, another Temasek portfolio company, last year agreed to acquire Keppel O&M.

The six former Keppel O&M executives are alleged to have paid bribes amounting up to US$55 million to win some 13 rigs-building contracts with Petrobras and Sete Brasil – two major oil companies involved in Brazil’s Operation Car Wash corruption scandal.