Why would anyone having a heart attack lock the door in two separate ways
I think you've misunderstood. The door has three modes which can be selected by the flight crew without leaving their seats - unlock, normal and lock. In normal mode the door is locked but can be opened from the outside using a touchpad. In lock mode it cannot be opened from the outside. It seems the door was in lock mode which is certainly very suspicious but it is not impossible for someone to lock the door then be taken seriously ill. I don't know if it is possible for them to put the door into lock mode accidentally, e.g. by knocking a switch.
the BBC article says that he was alive up to the point of impact and wanted to 'destroy the plane'
Yes, that is what prosecutors are saying. They may well be right. However, if you look at the history of crash investigations you will find cases where prosecuting authorities have jumped to conclusions before the investigation is finished and which subsequently turned out to be wrong. There have even been cases of prosecutors obstructing the experts who were trying to figure out what really happened. That is why I am concerned that the prosecutors appear to be running ahead of the investigation.
They don't seem to have any evidence for the assertion that the co-pilot wanted to destroy the plane. The only evidence they have given publicly to support their position is that the co-pilot was still breathing. If that is the case he was still alive but it doesn't rule out the possibility that he had become incapacitated. They say the co-pilot "presses the buttons of the flight monitoring system to put into action the descent of the aeroplane". That statement worries me. Until they have the other black box (which records control inputs) it is pure speculation. It may, of course, be that the cockpit voice recorder reveals the co-pilot shouting out his intention to crash the plane but they certainly haven't made that public.
Note that I am not saying the prosecutors are wrong. It is quite possible they are right. I'm just concerned that they are making these announcements before the crash investigation has reached any conclusions.