The police in Thiruvananthapuram, capital of the southern Indian state of Kerala, have said that "chance inhalation" of fatal amounts of carbon monoxide (CO) had caused the death of the three partying youngsters, including a girl in December last.
At that time three putrefied bodies were recovered from a closed garage, by the side of a car parked there. The news had sent had sent shockwaves in the city.
The police now say that the youngsters had pulled into the garage, owned by one of them, in a Maruti Zen car for a "quick and discreet" party around 3 p.m. on December 7. Ten minutes earlier they had bought a bottle of liquor from a nearby outlet. One of them had made a final call on his mobile phone at 4.45 p.m.
The girl was found dead inside the car while the bodies of two others were seen sprawled on the garage floor.
Possibly two had rushed out of the car at the last minute but could not manage to open the closed door of the garage.
They had all been partying inside the car with its windows rolled up and air-conditioning switched on, forensic experts said.
Petrol engines emit considerable amounts of CO, often up to 25 per cent of the exhaust gas. Most modern day vehicles, such as the Maruti Zen, are equipped with catalytic converters that minimise CO emission (CO is often a product of ineffective combustion).
The car was idling for more than an hour in the enclosed space and the engine got deprived of sufficient levels of oxygen needed for proper combustion.
Inefficient combustion and lack of proper ventilation caused lethal levels of CO to accumulate in the garage. The air-conditioning system sucked much of the deadly gas back into car's closed cabin space, causing the deaths of the occupants, the experts said.
The incident is in some ways similar to the death of three software engineers in Chennai in October 2006 when heavy rains had lashed the city. They had inadvertently inhaled lethal amounts of the carbon dioxide when their car was caught in a traffic jam caused by the flooding of the streets.