It would probably be easier for me if you told me what you have doubts about but here are some of my reasons:
I don't believe Santos at all; he has confessed to other crimes (claims he shot a man and police officer), he incorporated Angel Avila into his story after Avila's name was released in the press....so I totally do not believe the cartel hit theory....all the blood evidence as well, is pointing to one person as the killer. The horrific struggle is not indicative of a hit. WHO is going to kill children, someone that they could identify/Segura
the child support not being an issue. He says he initiated this process. That is not true. Court records show Brandi did. He claims Brandi and him were working it out. Not true she was also filing with the IRS to garnish his refund. The timing of his visit to Brandi, he has not seen her for months. He is also trying to get his other child's mom to reduce her support as well. He is not doing well financially. He is behind on his mortgage.
he asked two people for a gun the weeks before her murder, he has his own gun but suddenly it is missing, the snitch stated HG told him he hid the gun in his car motor, HG is trying to get rid of a car
his cell phone places him at the crime scene during the time of the murders, Brandi's cell has no activity, Brandi's cell is missing who has reason to take this, calling her with his number blocked
he lied about being home but his text messages from his wife prove she did not know were he was
he has had years to review all his case evidence and testimony to tailor his story
most crimes only have circumstantial evidence as this one does, there is enough for me to convict