An unreliable witness with a "play poker mentality" who refused to admit the truth until confronted with incontrovertible evidence.

This is how District Judge Ng Peng Hong described former BSI banker Yeo Jiawei in his grounds of judgment released yesterday.

Yeo, 34, was sentenced to 30 months' jail last month for witness tampering in a probe over the money laundering case involving billions of dollars allegedly misappropriated from the 1Malaysia Development Berhad (1MDB) state fund.

Yeo denied wrongdoing throughout his trial.

He was convicted on four charges of witness tampering. Witness tampering can carry a jail term of up to seven years and fines.

In his judgment, Judge Ng wrote: "Having considered the totality of the evidence, I was of the view that the approach taken by the accused was consistent with his 'play poker' mentality and I found him to be an unreliable witness."

At the trial, it was stated that Yeo had told his former boss, Kevin Swampillai, to "play poker" with the Commercial Affairs Department (CAD) if they questioned him.

The judge also cited other instances that showed Yeo's "lack of candour and credibility".

In court, Yeo repeatedly played down his connections with Malaysian tycoon Jho Low, who is at the centre of the money laundering scheme.

For example, Yeo initially said he did not stay in Low's apartment in Hong Kong in September 2014, but later said he spent a few hours there.

Likewise, Yeo initially did not recognise the name "Chuan Teik Ying", but subsequently recognised her as Low's girlfriend.

Yeo also could not recall flying on Low's private jet from Shanghai to Hong Kong on June 4, 2015, but later said that it could be possible.

Yeo had also claimed that he never met Low without another BSI banker, Yak Yew Chee, being present, but later acknowledged that he did meet Low by himself on at least two occasions - a badminton session in Singapore and a meeting at the Sandy Lane Hotel in Barbados.

Judge Ng said that Yeo should not be treated as a first-time offender as his interference with Swampillai and associate Samuel Goh, and the other interference with Amicorp employees Jose Renato Carvalho Pinto and Mun Enci Aloysius, were distinct offences.

"In short, he had multiple charges. Moreover, these two instances did not arise out of a single incident," Judge Ng said.

He added that Yeo's offending was aggravated since he sought not only to frustrate investigations into offences concerning him, but also CAD's wider investigations involving Low, and transactions worth billions of dollars.

Yeo still faces money laundering charges to be heard in court in April.