Hi! I am new here and wanted to weigh in and share my thoughts. I do not buy the drug angle at all, but based on what I could gather from Instagram... Danielle went to the pumpkin patch with her long distance bf's sister and his nephews 11 weeks ago. I am thinking that she was pretty committed to this guy. I think they may have met last spring.
I know nothing about FG, but based on what I've heard that others have been able to gather is that he seemed like a pretty normal guy. It is possible that if FG is in fact the person who committed the crime then perhaps he is a sociopath. Sociopaths can pull off being charming/blending in and yet still capable of doing heinous things.
I believe Danielle never made it into her apartment and I believe she left her purse in the car because she planned to run in and run back out very quickly.
I think it's possible that the FG may have talked to Danielle about his wife being sick and mistook her kindness for interest in him. I think it's entirely possible that she turned him down, but in his sick mind he may have thought if he wooed her enough that he might still stand a chance. Women hate confrontation, so it's possible that Danielle said the old line, "we can be friends" or maybe said to him, "if you ever need someone to talk to." He again probably thought that meant that he still had a chance, when really she was trying to let him down easily. He may have even weirded her out, but in her kind nature she still remained friendly and cordial which confused him even more. He may have tried to get her in his car by saying he "needed someone to talk to" because his wife is sick then when she refused his advances he then lost his mind and killed her or kidnapped her.
I also think it's possible that someone (FG or otherwise) saw an opportunity and took it.
The other theory is that he did stalk her and kidnap her etc. This is just my two cents!