Get Perper on the stand and ask him the right question. "COULD Anna have been murdered with these drugs??" There is no way, given all we know, that he can answer NO. It would have to be an "it's possible" answer.
Remember, his call of accidental is only an OPINION.
Trust me I know first hand that the coroner makes his call and the police can still investigate.That’s why I could not believe it when they said case closed.
What about saying there were no needle marks on her body.