Here's a motive for you.
The Manitowoc County Sheriff's office was in a storm due to SA's exoneration, for perverting justice and ignoring evidence. I'm sure it was already very embarrassing, and likely to result in loss of their jobs, and a heavy financial burden for the county. They were going to burn for it.
Manitowoc County Sheriff's Department wasn't sued. The County itself was sued. Aside from the county, only two people were named in the lawsuit: the retired former sheriff of MTSO Tom Kocourek and the former district attorney Denis Vogel. Colborn, Lenk, Remiker, Jost, Senglaub, etc... none of the cops who were actively searching Avery's Auto Salvage property were named in the lawsuit. None of them were under threat to pay anything.
Just because Avery sought a 36,000,000 dollar compensation, doesn't mean he would've gotten it. Even if he won the case, that doesn't mean he would get the amount of money he sought.
Avery didn't demand just $ 36,000,000. He actually demanded a minimum of $ 1,000,000 to a maximum of $ 36,000,000. If he had won, he probably would've gotten a reward somewhere inbetween. Could also have been less though...
The $ 36,000,000 obviously is based on the 18 years in prison, seeking compensation of $ 1,000,000 for every year spent in prison, x2. However, as I'm sure you know, of those 18 years he spent six years concurrently for the road assault on Sandra Morris. That's just one thing that probably would've prevented him from ever getting $ 36,000,000. Next it would've been difficult for him to prove intentional wrong-doing by MTSO, rather than, for example, negligence.
I highly doubt he would've received any reward that would make the county shiver. If you look at the financial reports of the county about that time they weren't doing half bad financially either. If Avery would've gotten a million or two, that wouldn't have bothered the county one bit. The county wasn't a self insured entity btw, it had an insurance carrier.
Even if the County, Kocourek and Vogel would have to pay Avery, I doubt anyone would be affected financially (except Kocourek and Vogel).
I no way do I imagine LE killed TH in this case, but I can totally understand the wheels were turning on how to make SA take the fall again, THEY HAD PRACTICE!!!
Or don't make the same mistake twice.
So if they found TH's RAV4, they could put a plan in action to save their jobs and reputations. They easily could have been watching SA given the scenario, or even had a camera on the yard, or had knowledge TH took pics for SA.
As much of a knave as SA is, him knowing DNA evidence was the reason for his release, how could he leave TH's bones outside his door? How could he put TH's license plates close to his trailer in another vehicle when they could have been thrown into a garbage can and lost forever.
I'll acknowledge it doesn't need to make sense in all aspects, psycho killers are not thinking or reasoning logically.
I would find it very unlikely that AC, upon finding the RAV4 on Nov 3, would suddenly decide TH was murdered and SA was responsible for it and then plant the car on Avery's property without yet knowing if he was the last person to see her alive. But this is something to discuss in another topic I guess... this one's about the key.