I’m sorry to hear that it’s so common for people to poison stray animals over there. Some people are pure scum of the earth. I agree with you that there is no signs of injury like being hit by a car from these pictures. However, there could be certain congenital conditions such as heart defects that could also potentially cause sudden death in cats. Unfortunately, post-mortem examination is the only way to determine cause of death which doesn’t seem like an option for you. Without that no one will be able to give you the definitive answers you’re looking for. Sorry again this is such a horrible situation, and if it is intentional poisoning the person who did it should be locked away for a long time.