The admitted confiscation of the phones is conclusive proof of corruption and obstruction of justice if the video was deleted.
Under the law, given this scenario, all reasonable conclusion will be made against those who took the phones and erased the video.
If the cops did nothing wrong, they would not have confiscated the phones.
The confiscation of the phone may not show anything. To my knowledge, there's no electronic trail of what's done on the phone if it does not involve communications. The way flash memory works is that there's no way to figure out whether something was recorded and deleted or if no recording was made in the first place. And if something was deleted, there's no way to find out who did it or when.