The investigation into the Stockline plastics factory explosion took thousands of man-hours and almost two years to complete.
Thousands of tons of rubble were removed from the scene
As rescuers were arriving at the scene, Health and Safety Executive (HSE) investigators were already starting to piece together what had happened.
The blast at the Glasgow factory caused Scotland's worst workplace disaster since the Piper Alpha oil platform disaster in July 1988.
For the first time, the procurator fiscal launched a joint investigation with police and the HSE.
Police or the HSE usually investigate and send a report to the fiscal to decide whether charges should be brought.
The scale of the incident, the number of fatalities, serious injuries and families affected meant a joint investigation was needed.
Catherine Dyer, area procurator fiscal for Glasgow, said: "It was fairly unique because it was the first time the police, Health and Safety Executive, Crown Office and procurator fiscal service have joined forces in a case like this."
Thousands of tonnes of rubble had to be cleared from the site every day, after the bodies of the nine victims were recovered.
Documents from the factory were strewn over the site and police were tasked with collecting and logging every one.
Health and safety experts then began their investigation into the explosion.
Evidence was sent to and examined at the Health and Safety Laboratory in Buxton, Derbyshire.
The investigation led to an liquid petroleum gas pipe which had corroded, leaking propane into the cellar of the factory.
It then ignited and caused the blast.
Although the building was referred to as the Stockline plastics factory - due to the signs around the building - the factory was actually owned by ICL Plastics Ltd and the work that took place there was for ICL Tech Ltd.
Stockline Plastics was the distribution company and was not involved in any manufacturing.
After thousands of hours of investigation, charges were brought against ICL Tech and ICL Plastics in February 2006.
It was decided that the companies rather than any individuals would face the charges.
The charges, under the Health and Safety at Work Act, centred on ICL's failure to ensure their workers were not exposed to risks of personal injury and death from fire, explosion and other dangers.
The companies were also accused of failing to carry out suitable and sufficient risk assessment in relation to their employees.
Ms Dyer added: "There was a lot of legal technicality to look through in something of this size to decide what the appropriate charges were."