I'll tell you what perplexes me most about this case, and it's the K-9's and unknown crime scene/method of transportation (besides Lucas being missing in the first place, of course).
I'll have to dig up the quote about the dogs. If I remember correctly, dogs were used to search the house. I don't believe it said air scent dogs or cadaver dogs or both. I also don't remember if it specifically mentioned the car being searched, but I'm guessing no, because we didn't even know what she drove until our VI told us. That doesn't mean they didn't search it, it just means LE didn't tell us and/or the media didn't find out AFAIK.
So, that leaves me to think the crime was likely not committed in either the apartment or house, and he was not transported in EG's car. Remember, a WS'er gave us a link which told us there is just a tiny window, I believe 2 minutes, before a deceased body starts to emit gasses that a cadaver dog could hit on. I guess it's possible EG could've killed the poor boy in the car if she was in a rural area, and immediately discarded him. But from what we know I think the likelihood of him dying in the apartment, house, or car is very small.
This gives me a tiny shred of hope that someone besides EG knows something happened and could come forward with info leading to Lucas' whereabouts. But as time goes on it seems more and more unlikely.
I think perhaps she was high at someone's house, and had both kids with her. Something possibly happened there...Lucas just looking at her wrong might be blamed for messing up her "high" and dealt with harshly. Whether there was even a single witness I do not know. He was likely discarded within walking distance of that location (might've been an abandoned house or property IMO)...or, she borrowed someone else's car (with or without their knowledge...if a fellow druggie was high as a kite she might've been able to snag keys off a table or already in an ignition and taken off to dispose of Lucas).
This is my top theory based on what we know or think that we know. If not for the child endangerment charges stemming from an incident involving drugs, I don't know what theory I could come up with.
JMO.