I have one baaaad guppy on my hands!

He is an orange devil!
He is the first fish my daughter got for her 5g tank (now a
betta tank) and has been living in my 30g "bachelor pad" for a few weeks now. Since the move he has taken over that tank, chasing the other fish and forcing me to move two fish because I thought he would hurt them!
We finally decided to make that tank my daughter's guppy-only (with the exception of her 2 bloodfin tetras who are laid-back) tank which she named the "guppy train"
Anyway, she added 4 guppies to the tank, making a total of 7 guppies and the 2 bloodfins...
The problem is that 2 of the new guppies are lyre-tailed and after 48hrs in the tank, one of them only has one fin left!!
Clearly

has struck again!
I just got the 2 lyre-tails of that tank and put them over in the "zen garden" 30g with my male platies and mollies. I am hoping that they are not mean to him so that he can recover quickly. I feel TERRIBLE that this has happened to him and I just dont know what to do about that Devil Guppy.
Has anyone dealt with a super-mean fish like this before? Is there any way of chilling him out so he doesn't beat up his tankmates? So far the other guppies are doing fine, but I am afraid that will change. And I do not want to add any more fish until I know they will be safe.
My last-resort is to put

in a 5g tank by himself or with one of the guppies he is fine with. Or maybe the betta??

(kidding!)
Any advise would be very welcome...
