Fireworks cleared of blame for M5 crash.
Just after the incident in November, police claimed the crash may have been caused by smoke from the display at Taunton Rugby Club drifting on to the motorway.
But meteorologists, pyrotechnic experts and crash scene investigators set up a reconstruction of the crash scene in an empty aircraft hangar and it found fog was the most likely cause.
Their reconstruction proved the south-westerly wind that night would have blown any smoke from the display away from the road.
Instead, they believe a driver braking suddenly as they hit a dense bank of fog is the most likely cause of the tragedy.
Avon and Somerset assistant chief constable Anthony Bangham had pointed the finger of suspicion at the rugby club and Geoff Counsell, boss of Firestorm Pyrotechnics.
Lawyers representing the club and Mr Counsell are still considering whether to take legal action or make an official complaint against Bangham.
A source close to the investigation said: "It's been an incredibly complex inquiry and it's still hard to be absolutely categoric about what happened."
Police will pass their file on the crash to the prosecutors in the next fortnight and a final decision on whether there will be any charges is likely by the end of May.