I'm going to take a wild stab at motive now. I wasn't seeing it before. All of this is MOO. The grain of truth in the lies may be that KB was getting weary of commuting to Pueblo from WP. Long commutes in heavy traffic are stressful. Had she sold or rented her condo and moved closer to work, PF and SF would have had less time with baby K and KB might have made other child care arrangements that did not include SF and may have resulted in PF having to pay child support. IMHO, SF in particular had bonded with little K, and PF was at least OK with the arrangement they had. So, PF investigated the possibility of getting full custody. In doing so, he determined that unless he could prove that KB was an unfit mother, that was not going to happen. So he started spreading lies about little K having burn marks on her hands, KB shutting the refrigerator door on her hand, KB being a terrible mother, etc. But he knew he'd need proof and he didn't have it. So his mind went to another, treacherous way of getting custody of K - by murdering her mother.
I wasn't seeing custody as a motive before because CB said that KB loved her job. And KB had purchased the townhome, so I assumed that she liked the area, loved her job, and wanted to stay. But it makes sense to me that after commuting to Pueblo in heavy traffic for several months, and also trying to care for an infant, that she needed to make a change.
All MOO
I am interested to see what the DA thinks. But it will probably be a long while before we know.