How much money was in the trunk? In the clown pictures?
I counted the stacks in the one clown picture when Roy takes out money to give to his mother - there are 18 stacks (16 left after he takes out two). Normally, stacks like that are 100 100 dollar bills = $10,000. Roy's stacks are of 20 dollar bills, so there's $2,000 in each stack. This makes sense in that he takes out two stacks to give to Lily, and tells her it's 4 grand.
So, if we assume that the other clown picture is equal to the first, if there's, say, 40 stacks in total (18 in one picture, 22 in the other), that's about $160,000, give or take. Not too shabby an amount to have saved up in 8 years - from the time he goes out on his own at age 17 to age 25. Roy's saving 20 grand a year.
How much is in Lily's trunk? It didn't look like anywhere near as much. Fewer stacks. But they were stacks of 100 dollar bills, so each stack is 10 grand. I didn't get a chance to count how many stacks were down there, but if there were 15 stacks - and it sure looked like there were at least that many - then she's got roughly the same amount in the trunk that Roy's got in his pictures.
Now here's the thing. "Lily" is dead. The police will investigate the source of "Lily's" money. They will come up empty, because Lily doesn't have a record. (I find this dubious for someone who's been a career criminal for at least 20 years. But I can go with it.) So, after some amount of months, the investigation is complete, and Lily's money goes to her next of kin. That's Roy.
Roy's not in need of any cash - he's been diligently saving his money for years. Lily knows how much money she has; she can see how much money Roy has. It would basically be an even swap. Why doesn't Lily tell him this, and avoid trying to bash his head in?
"Listen, Roy, I've got about the same amount of money in my trunk as you have here. It's not as if you're using this money for anything; it's just sitting here. I'll swap you mine for yours. You'll get my money after the cops finish with their investigation. It'll just be a coupla months. Think of it as a loan, and you know I've got all the collateral. Whaddaya say, Roy?"
That would have worked.
I want the doctor to take your picture so I can look at you from inside as well.