I think there's a fair argument that the destruction of potentially exculpatory evidence creates per se reasonable doubt. I.e. there is no incriminating evidence that can remove any reasonable doubt that the exculpatory evidence may have proved their innocence.

Another issue is that due process has been broken in a way that can never be restored. I'm a little leery of continuing prosecution under those conditions, given that due process is the underpinning of a just legal system.