One other thing. How often do you see somebody that is sentenced to life imprisonment, whom has also extinguished all possibilities of getting another trial and is left without a lawyer, get 20 fucking boxes of trial documentation and start studying it by himself to try to prove his innocence?
For me this, almost more than anything else said in the documentary, proves to me that Steven did not do it.
And to me, the most logical explanation is that the police did it.
My theory is that the police decided that they had to frame Steven at all costs and started surveillance on him. Then they figured that Theresa was going to visit him on that day and decided that if they would plant evidence of her killing at his property, that, together with little more manipulative tactics, would be enough to get a jury (who knows if also set up and coerced) to convict him. Then, after they killed Theresa, they looked at the actions from Steven on the day of the murder (made a bonfire, etc.) and fabricated the evidence in the most "logical" and "believable" way they could. Still, for me they did not achieve their goals because all planted evidence is so fucking obvious but they managed to convince the jury and for that they placed all their most corrupt people on the job to make it happen.
The brother is an asshole although blindly, he just wants to find who did it and probably police and prosecution acted as their best friends from minute one, so he was unable to go against them. Same with the ex-bf, I don't think there is enough evidence to prove him guilty but at the same time they never tried looking for it, so who knows....