Where's that smell comming from?

A friend of ours who is a Tradie uses his 4wd Wagon for a work vehicle, anyway he took 10 days off for is holidays recently, so the day before they were going away he decides to go fishing, he fishes all day he catches a heap of fish and cleans and guts them at the beach, he decided to keep the fish heads and guts for the next fishing trip, and leaves them in two 20ltr plastic buckets, he put the filleted fish in the esky, when he arrived home he takes the esky out and forgets to take the plastic buckets out of the 4by, he and the family go on holidays, and while he is away things start to deteriorate in the 4by, his next door neighbour smells this odour in the air and thinks it is in his ceiling, maybe a dead rat or something, the family come home after 8 days away, and cant work out where or what the smell is or where it's comming from, now he hasn't been near the 4by until he was ready to go back to work, as it was parked in the front yard near the boundary fence, yes he opens the car door and Whamo, he staggered backwards and gasping at the same time, the 4by has been in the sun for 10 days with two buckets of fish guts in it, the whole interior was Fly Blown, he promptly got the the buckets out and tried to decontaminate the vehicle, he tried all sorts of treatments, there were maggots comming out of every part of the vehicle, his mate suggested to call the insurance company, they said it was covered and so they sent an assessor out to inspect the vehicle, yes they wrote it off.

Cheers