So what do you think the cause of death actually was then? Malnutrition, pneumonia? Do you think he took the reported walk just beforehand? I know there's scant info on this, but I'm very interested in your best guess/assessment
Penal administration regularly denied him medical treatment and even access to his lawyer. In 1000+ days spent behind the bars, Navalny's health greatly deteriorated. He fell critically ill several times.
The authorities formally sealed his fate in december when the decision of relocating him to one of Russia’s northernmost prisons was made - well above the Arctic circle. That fact alone meant that keeping him alive was no longer a priority.
He spent most of his time in a special area of the penal colony - a prison within a prison if you will. A place normaly designed to hold and break incarcerated individuals considered to be security risks to other inmates or staff - as well as those who violate facility rules or are deemed disruptive.
Anything could have been done to him under those conditions. Absolutely anything. However, his legal case still required regular hearings conducted via videolink. So that rules out the most extreme forms of abuse ( around the clock beatings, stress positions, anal rape with different objects etc..)
In my opinion, the easiest and cleanest way to get rid of him was to simply wait until he collapsed sooner or later due to poor health, and call the paramedics "too late." Exotic lethal tools or substances were simply not needed in such a harsh and remote environement. Extremely low temperatures are already widely used as a form of physical abuse in those places.
Again, he was formally deemed expendable in december. He was a dead man.
According to propanganda news outled "RT", Navalny died of a blood clot. The true causes of his death are "formally" under investigation.