Thank you to everyone for posting so many interesting theories about this mystery.
It's been fascinating to read about your individual personal experiences regarding h/s graduation and parties. Those personal experiences have helped to create many possible scenarios and I know it's helped me to think outside the box and develop even more theories.
I want to throw a few things out here and see what you all think...
News articles have mentioned that Suzy and Sherrill had a very close mother-daughter relationship and were very good friends.
So... Suzy and Stacy show up at Suzy's house around 2:30ish. Sherrill isn't expecting them and she's in bed. Suzy and Stacy go to Suzy's room. Suzy sets her purse down and Stacy sets her purse next to Suzy's. This could be possible because as a guest, Stacy might 'copy' Suzy... Stacy hadn't spent time there and would do what Suzy did.
So... now the girls are home (and both purses are on Suzy's stairs). Sherrill hears them come in (possibly peaking out the shades when she hears their cars pull up to the house). Sherrill gets out of bed, grabs her purse (many women smokers keep their cigs in their purse), lights a cig, and heads to Suzy's room to chat with her daughter and friend. (Bart and others have said that Sherrill was a heavy smoker and it was the first thing she would do when she woke up- Having been a heavy
smoker myself, I can attest to the fact that you do grab a cig almost without even thinking about it)
Going into Suzy's room- to say hi and see what's going on- she sets her purse next to the other two (probably not thinking much about it), smokes her cig and chats with the girls. Maybe asking how their night was, hearing funny party stories, etc. From my personal experiences, two girls coming in from graduation night and parties ARE NOT going to come in, get ready for bed, and jump in bed to go to sleep. They're going to talk about the night, boys, or whatever. They might grab some munchies and a soda. Maybe they're not going to be ready to call it a day, yet. At least that's how my friends and I were- we'd go a hundred miles an hour... even if we had plans in the morning, we'd still keep going and going and going... just having fun and laughing and stuff.
I've had several thoughts about the purses- and again this is from a personal perspective, but if I were one of the many people who entered the empty house, I wouldn't grab the purses and stack them all together on the stairs to Suzy's room. IF (and that's a big IF) I were to move the purses, then more than likely it would be to a table or someplace like that where I could search them all together... but again, I don't see this being something someone would do (I wouldn't be comfortable doing it)- at least not early on.
I can see the McCalls grabbing their daughters purse (and whatever else of hers was there) and moving her belongings around. A lot of concerned parents would do that. But I still can't see where the McCalls would be comfortable rifling around through Suzy and Sherrill's purses... I think they would notice the other purses- becoming more alarmed as more time went by- but I still can't find at what point someone would start moving the purses around.
I'm leaning towards the theory that the missing women themselves left the purses on the stairs...
A few other things that make me wonder....
Only Sherrill and Suzy live in the house and they've only lived there a few months. Nobody would know what-if anything- was missing from the house. An example would be shorts/sweats/sleep pants for Stacy. Mrs. McCall, being very upset, would think that Stacy was only in her shirt/panties because Stacy's shorts were there, but no one would have any idea if Stacy was wearing something else.
Other items could be gone, but no one would know because no one else lived there.
One more thing- and then I'll stop
We can't even be sure that Sherrill was in bed- the time of night and the fact the the bed looked slept in leads us to believe that she got out of bed for some reason that night. But, not everyone makes their bed every day. I'm embarrassed to admit, but as an adult, I have very rarely made my bed, in fact the only reason it gets made now is because my husband does it every morning
So Sherrill could have been in the living room watching tv or whatever when the girls came home... and Sherrill's parted bedroom shades could have just been shades that were 'stuck' that way...
Thank you for reading my ramble! I read A LOT more than I post and I have learned so much from so many of you great sleuthers!