Its a bit wierd another poison happened at the Asian restaurant. He did that so he can look like a hero for JJ.
I think he did it to get back at Karl, as Karl worked their and reported him to HR. Leo was just the collateral damage.
Then when JJ was poisoned instead, he decided to do another poison to get back in everyone's good books.
If he did do it to Leo on purpose, maybe it was David related.