The killer was going to prison? The killer had alzheimers? Took the case away to avoid detection? Kept the Angels body separate to avoid detection? Kept the child captive while Karlie was in prostitution? Ransom? Desperation? Angel got to school age, and authorities would start tracking records? Authorities start looking at 6? Karlie wouldnt have had a mobile phone, not under her name any rate. Having phone and banking records will be the tell tale for police. Not to mention clothing purchases.