So I have a few theories. 1) Daniel Wade Moore and Dr. Tipton were gay lovers and conspired to kill Karen Tipton. 2) Moore and the Tiptons had previously engaged in some form of groupsex and Dr. Tipton walked in on Karen and Daniel. Since Tipton is gay for Daniel, he spares him but kills his wife. 3)Most likely scenario: Moore and the Tiptons had previously engaged in group-sex. Moore and Dr. Tipton became gay lovers. Perhaps, Karen was having her own affairs with other people like Dr. Tipton's best friend OR Karen threatened to out Dr. Tipton and his gay lover, Daniel Wade Moore. They conspire to kill Karen for whatever reason. Daniel Wade Moore was at the residence to pretend to set-up another threesome or pretend to fix the alarm in order to keep Karen from picking up the kids. Dr. Tipton also could've said he was going to pick up the kids that day. Instead, he went home and violently stabbed his wife to death with Moore as an accessory to murder.
Daniel Wade Moore exhibited very guilty behavior (confession & stabbing himself multiple times) and there was forensic evidence that he was at the scene; however, he never confessed to actually stabbing her. Moore can't say he saw Dr. Tipton stabbed Karen because that would implicate himself and set himself up for possible conspiracy charges. Dr. Tipton was the one that stabbed his wife, so he's going to get away with murder as long as he doesn't confess to the stabbing and say Moore was there with him.