I keep seeing the Dogwood Festival mentioned, but no mention of a possibly much more significant festival: 4/20.
April 20 is THE pot holiday. These folks were killed the night of April 21/22.
I live in southern Ohio and 4/20 is celebrated here, especially in rural areas, with cookouts, bonfires, and sometimes very large parties, often all day/into the night parties. A younger relative of mine went to a 4/20 party about 5 years ago. It was held in the country, only about 75 miles from these murders in fact, at a property with a huge barn on acres of land. There were hundreds of people there, many of them camping in tents in the fields; there were local bands playing in the barn, people grilling and selling food, and (I can only imagine!) people selling weed.
If (if) the Rhodens' grow operation is related to these murders, I can think of 2 potential reasons offhand why the date might be significant:
1) Robbery.
I am not a 'pot culture' person but I am a former gift shop owner, and from all I've heard, I imagine 4/20 is for pot dealers what Christmas is for retailers. There is probably a big uptick in sales in the days leading up to it. Not to mention the day of.
Possibly, someone(s) thought that one day after 4/20, the Rhodens would be sitting on a huge pile of cash they hadn't yet had time to spend, or to launder or whatever.
High-quality weed goes for $300-$400 an ounce in this area. Source: weed websites, plus confirmation by previously-mentioned relative who bought an ounce a few months ago. Let's call it $300 to be on the conservative side. That's $4800 a pound. Do 'only' 200 plants still sound like a 'small' operation, as some here have called it?
[Side note: I don't know much about growing so these numbers could be slightly off, but if you get a pound per plant, and harvest said plant say 3 times a year, that's $14,400 per plant. Multiply that by 200 and it's almost 3 million dollars a year. That's retail price for high quality stuff, minus costs, etc. but STILL.]
Back to the 4/20 scene: one kid with a backpack full of $20 baggies walking around a big party could make thousands of bucks in a short time. Multiple said kid by x number of other people at other parties in the region, or even in other states, and that adds up fast.
It doesn't matter if the Rhodens sold retail, or made bank that day or not. All it would take is for someone to believe that they did.
The problem with robbery, of course, is that it's pretty extreme to kill 8 people at 4 locations in order to accomplish it -- including a 19 year old girl asleep with a brand new baby, ffs. In fact, it's guaranteed to draw huge attention to your robbery, and would be utterly stupid. But then again, maybe it was a robbery gone really, really, really, inevitably escalatingly wrong somehow.
2) Unpaid debt / cartel.
If the Rhodens owed someone a lot of money, they could have said, 'Give me till after 4/20 and I will have it.' Then something went wrong -- a problem with the crop, someone siphoning off the sales, who knows what. Then comes the night of 4/21, and the reckoning.
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These are only thoughts, and I have no idea if the grow operation is even related or not. TONS of people grow weed and do not get murdered. But it's notable, IMO, that these murders didn't occur in early April, or weeks after 4/20. It was effectively 24 hours after the big day.