Family Dollar has a history page on its site:
http://familydollar.com/history.aspx
...and in picture #4 at the link below there's actually a good picture of a 1970s-era bag. It's brown and while I can't tell whether it's paper or colored plastic, the letters are uneven, unlike the straight line of letters on the crime scene bag. Also, the logo in the parking lot photo (#5) looks essentially the same as today's Family Dollar logo. The "A" is very distinctive with a break where the left side of the horizontal bar meets the leg of the "A," plus it overlaps the letter "M" a bit. The "A" on the crime scene bag appears entirely detached from whatever the next letter is. Unless FD had another logo in use in the 1980s, I doubt this is their bag, as you'd think the corporate office would issue the same bag for every store in the chain to keep fonts, logos and slogans consistent across the chain.
http://familydollar.com/images/History1970Big.jpg
More thoughts on the bag itself: It appears to be type #2 plastic, maybe the "t-shirt bag" style, commonly used for groceries, take-out food, and lightweight items. Most department stores, at least nowadays, offer the stronger type #4 plastic bags. They're shinier and tougher. In my previous post I suggested Famous Footwear but now I'm not so sure a shoe store would offer a flimsy type #2 bag to carry pointy-cornered shoe boxes that might tear right through. I'd think FF would have a type #4 bag for customers that wanted one. Most mom & pop, non-chain stores I know don't even print their own logo on bags. They either use the generic "Thank You" or smiley face type #2 bags or plain white, black, etc.
This is a "WAY OUT THERE" idea, but so is the author of this post.
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
I used to work at a thrift store and annoyed my coworkers in the clothing department whenever I'd find a donated outfit with a hanger or tag from a long-closed business. ("Zayre's! That closed when I was still in grade school!") People do hang onto clothes for decades, in some cases, before they realize they won't wear them again and donate them. We got a lot of clothes still on hangers with the paper wraps from long-closed dry-cleaning businesses, and invariably the belts and accessories to the outfit would be stored in a plastic grocery bag and hung on the same metal hanger.
If someone could print out a poster with the bag and a short explanation and offer a "bounty" for any thrift store worker who can find a matching bag amongst donated items, maybe it could be hung in the Berks County thrift stores and maybe someone could help us solve our bag mystery.