I am extremely distraught, so please forgive my rambling and errors. Edits are welcome.

Yesterday, before I got home, my wife called to tell me that she found our son choking our kitten that we've had for about 3 months now. The cat seemed to be almost passed out, but recovered after being let go (although it was coughing continually for some time after).

This is the second time something like this has happened, but neither of us witnessed the first time, we only heard the cat yelping, and when we rushed to see what was happening, our son claimed that he was choking the cat. We made it very clear that the cat could die and that if this ever happened again, we would have to give the cat away to keep him safe.

There is already a similar-sounding question that was answered here, but there are several reasons I think that the top voted and accepted answer does not apply to my case:

It quotes Child Bereavement UK, saying children 2 to 5:

Often struggle with abstract concepts like ‘forever’ and find it difficult to grasp that death is permanent. Their limited understanding may lead to an apparent lack of reaction when told about a death.

This is not at all plausible, given that my son's little brother passed away shortly before his due date because of medical complications. He only got to see his little brother once at the hospital. He still remembers this event and talks about it occasionally. He completely understands that his brother's death is permanent, and does not expect him to come back.

Secondly, in the past year, both my grandmother and uncle have passed away. It is the same with both of them. He understands perfectly well what death means in these cases, so why wouldn't he understand death in the case of an animal?

Thirdly, his mental development is extremely advanced for his age. His vocabulary, understanding of the internals of mechanical objects, and even of social norms is far beyond his age. We receive comments from other parents about this routinely.

For these reasons, I reject the idea that he doesn't know what he's doing. He said that he did it because he was mad, but according to my wife, he didn't seem mad about anything leading up to the incident, or even afterward. EDIT: Either I misunderstood the first time, or my wife changed her story, but he may have been angry before the incident due to my wife yelling at him to stop chasing the cat around the house.

I wouldn't be anywhere near as upset as I am without this additional piece of context: after this incident with our son yesterday, my wife admitted that she herself killed a cat previously (while we were already married) and lied about it, telling me that it had fallen asleep in the open washing machine, and that she turned it on not knowing it was inside. In reality, she choked it to death with her foot against the floor, and covered it up before I got home.

She claims that she doesn't know why she did it, but that she had an irrational hatred for the cat at that moment, and has felt extreme guilt about what happened. This occurred 6 years ago (2 years before either of our sons were born). My wife has no criminal record, nor have I ever experienced her being violent towards people or animals, so this is a complete shock to me.

Her admission only came about because she fears our son has somehow inherited something from her that has caused this terrible behavior.

My own marriage problems (which I didn't think I had only a day ago) are obviously outside the scope of this question, but what should I do in the near term about my son?