I've been away from WebSleuths for about two years due to health problems and decided to take another peek.
I seem to recall that at some point, maybe about 18 months to 2 years ago, there was a report from an independent agency that was asked to evaluate the handling of the case by the Evansdale PD. The subsequent report compared the response of the EPD to the guidelines issued by the FBI for investigating child abductions and found that overall the way the case had been handled was well above standard.
Tangential thought: the methods by which law enforcement solves homicides in this country tracks closely with the statistics for who commits the homicides. The most common killer is someone that the victim lives with or knows well and the most frequently solved homicides are those where the killer was someone who lived with or knew the victim well. The least common form of homicide is stranger homicides, those where the killer has no known social ties to the victim, and the least often solved type of homicide are those where the killer is thought to be a stranger.
The general strategy of investigation, where LE starts with the victim's inner circle and only moves outwards when the inner circle is (more or less) ruled out heavily favours solving the most common type of homicide.
So, my point (altho' I"m not sure I have one) is that Lyric and Elizabeth were most likely abducted and murdered by a stranger to them or by someone who had only a very casual acquaintance with either them and/or their families.