You have made yourself a party to it already.
You're really the MAIN party to it.
"But do as you like," he goes on.

"I'm giving him more chance than I ought to with those pills.

I might shoot him, and I would, and then face the music, if it wasn't for mixing the children up in the scandal, Jane.
If you want to see him get a fair chance, Jane, you've got to hand out these pills, one to him and then one to me.

YOU must kill one or the other of us, or else _I_'LL kill HIM the other way.

And YOU had better pick one out for him, because _I_ know which is which.