Executives from five Singapore-based Japanese firms would gather almost every month for what were sometimes called "Asean SM Meetings" or "President's Meetings".
These turned out to be cartel meetings to fix the price of a tiny electrical part that the firms sell in South-east Asia, and went on for over 20 years going back to 1997.
Over four years, a team from the Competition Commission of Singapore (CCS) pored through thousands of documents and conducted extensive interviews with senior executives from the firms.
Earlier this month, the commission announced it had cracked its biggest case yet in terms of the record $19.5 million fine meted out.
It took so long that three out of the five white-collar sleuths assigned to the case had changed jobs or left the CCS in the four years.
The team's leader Serene Seet, 37, said: "We ran out of storage space - it was easily more than 10,000 documents in the end."
The marathon probe began with a tip-off from Panasonic, one of the five firms, in October 2013, in the form of a leniency application.
Team supervisor Harikumar Sukumar Pillay, 40, director of the enforcement division at CCS, said he was excited as he noticed Panasonic had filed similar applications in Europe, Japan and the United States - showing the scale of the activities.
As Panasonic was the first to blow the whistle, the CCS team had to ensure its anonymity. It allowed the firm to submit information in writing and redacted incriminating evidence during the probe so that other firms would not know who had given them away then.
By May 2014, the Singapore team had enough ammunition to formally launch a probe. The team zoomed in on four others: Rubycon Singapore, Singapore Chemi-con, Nichicon (Singapore), and ELNA Electronics.
The tiny item at the heart of the commission's largest case was the aluminium electrolytic capacitor used as part of electrical circuits in products like computers.
The five firms held more than two-thirds of the market share in Singapore for these capacitors.
Cartels among suppliers cause serious harm to competition in the market, leaving buyers in a poorer bargaining position and likely having to pay more for goods.
Two months after the launch of the probe in 2014, Rubycon, applied for leniency. Singapore Chemi-con and ELNA soon followed.
Ms Seet told The Sunday Times: "If you want to get involved in a cartel, you have to watch your back because anyone could whistle-blow and get the rest of you in trouble. So that's why applying for leniency is a race to the door."
As the investigations involved firms headquartered in Japan, the CCS had to get senior executives to fly to Singapore from Japan for interviews that sometimes lasted more than 12 hours.
Said Mr Sukumar Pillay: "The interviews could begin at 9am and end at 10pm because the executives needed to leave the very next day."
Said Ms Seet: "A lot of them were more comfortable in Japanese, so we had to bring an interpreter in."
THE FIVE LARGEST FINES IN CCS' HISTORY
Year of fine: 2018,with the following breakdown: Singapore Chemi-con: $6,993,805, Nichicon: $6,987,262, Rubycon: $4,718,170 and ELNA: $853,227. Panasonic escaped the fine because it was the first to apply for immunity under CCS' leniency programme
What happened: Five electronics firms met regularly since 1997 to fix prices for aluminium electronic capacitors sold in South-east Asia.
BALL BEARINGS MANUFACTURERS
Year of fine: 2014
What happened: Four Japanese ball bearings firms engaged in a price-fixing cartel from 1980 till 2011. They met regularly in Japan and Singapore to agree on prices to protect their market share and profits.
Year of fine: 2014
What happened: A cartel of 11 freight forwarders plying shipments from Japan to Singapore fixed certain fees and surcharges, and exchanged customer and price information for freight forwarding services for shipments on the Japan-Singapore route.
BUS OPERATORS AND TRADE ASSOCIATION
Year of fine: 2009
What happened: 16 coach operators and their trade association agreed to fix the prices of coach tickets for trips between Singapore and various destinations in Malaysia from 2006 to 2008.
Year of fine: 2010
What happened: Sistic forced 17 event promoters, the Esplanade and Indoor Stadium to sign exclusive contracts with it, so anyone who wanted to watch a concert or play had to buy a ticket from Sistic.
NOTE: THESE AMOUNTS WERE THE INITIAL FINES IMPOSED BY THE CCS, BEFORE THE RESULT OF ANY APPEALS.
Investigations were marked by civility, she added, and there was no raid involved, though this was carried out in other cases. The CCS team would ask for documents, and would receive boxes of them in return.
Mr Sukumar Pillay said how much a firm cooperates with a probe plays a part in how much of a discount it gets on the final fine.
"The companies and legal counsel were facilitating the attendance of the individuals whom we might not have been able to reach otherwise, because they reside outside Singapore's jurisdiction," he added.
Slowly, the CCS team uncovered more than 20 years of collusion, with regular meetings in Singapore to manipulate the South-east Asian market. Similar meetings were held in Japan from 1997, the results of which influenced the actions of the firms' staff in Singapore.
By February 2009, Panasonic had issued an internal notice barring its members from attending the cartel meetings, and together with ELNA, stopped attending them.
The other three firms continued to meet to fix prices until March 2013, sometimes referring to the gatherings as "dinner meetings". The last recorded meeting took place on March 25, 2013.
Ms Seet said she was not surprised by the final figure of the fine as the CCS followed a very strict calculation methodology.
The watchdog considers factors such as the duration of the crime and each firm's revenue to determine the amount of the fine.
The probe was the first for Mr James Yoon, 29, who joined the team in mid-2015 to replace someone who left and was in charge of calculating the final sum.
"Because we knew this would be CCS' biggest fine to date, we were concerned about our calculations, wondering whether our methodology was robust," he said.
"I definitely went through the numbers more than 20 times."
For being the whistle-blower, Panasonic's fine was waived. Nichicon did not apply for leniency. The discounts received by the three firms that did are not known.
Said Ms Seet : "In this case it really paid (off) for Panasonic... And even for the rest, an up to 50 per cent discount is a lot, right? The fines would have been much higher had they not come in for leniency."
While it is a historic case for the 13-year-old CCS, the team knows its work is not over yet.
The firms have till March 6 to file an appeal, and Ms Seet said settling that could take up to 23 months.
However, she said: "I'm happy to have seen it from the start till now. And if it goes to the appeal stage, I'll probably see it till the end."