Alcohol was a major factor in the riot in Little India on December 8 last year, said the lead investigator of a public inquiry into the mayhem which closed on Wednesday.
Contrary to suggestions by some groups, the investigating agency found no "deep-seated unhappiness" among the foreign workers involved who were interviewed afterwards.
These were two key observations made by Central Narcotics Bureau director of investigations Adam Fashe Huddin, 47, who gave the Committee of Inquiry (COI) a wrap of the evidence he and his team of five officers had gathered in their probe on Wednesday.
The bureau was tasked on Dec26 with conducting an independent investigation for the COI, which has ended after 24 days of hearings from 93 witnesses.
Mr Adam, a 22-year veteran with the bureau, said 324 interviews were conducted for its investigation, video footage reviewed and 11 site visits made.
The investigating team, together with the COI, also visited dormitories and other foreign worker enclaves such as Geylang.
Mr Adam acknowledged the lack of "direct evidence" pointing to alcohol as a cause of the riot, but officers on the ground had observed rioters "losing their balance and smelling of alcohol".
"Alcohol bottles were literally raining at police officers," he said.
As proof of how much drinking there was, he cited revenue losses among Little India liquor stores now that alcohol sales are restricted. One, he noted, is losing as much as $25,000 every Sunday.
The probe did not uncover any "widespread and systemic abuse" of foreign workers that might have led to them to "take the opportunity... to vent their anger".
There were no complaints of delays in salary payments or poor living conditions from any of the foreign workers interviewed before they were deported in the riot's aftermath, nor among those charged for their roles in the riot.
Rather, the trouble was sparked by a confluence of factors after a fatal traffic accident involving a worker. These included a misconception of inaction by the authorities to rescue the victim, and pent-up frustrations against the timekeeper, and auxiliary police officers, who issue fines that form a large part of their wages.
Mr Adam suggested the Land Transport Authority could regulate the two bus associations that run private buses ferrying workers between their dormitories and Little India, extending the service to Sunday mornings and Saturdays to even out the crowd.
He said: "This will help to reduce the impression that foreign workers were being denied the opportunity to visit Little India, as has been the case after the capacity of buses was reduced and operating hours curtailed from 11pm (previously) to 9pm."
Mr Adam also proposed training for the bus timekeepers and coordinators to minimise friction with foreign workers. Auxiliary officers could also be better educated of their roles, and foreign workers with social norms here.