there was a documentary on this on chanel 4 about a year go, it concluded that senna's williams was bottoming out, it bottomed out as he reached the corner and he lost control, the programme makers had footage, and telemetry given to them directly by the williams team. On board cameras showed that the steering wheel was moving about, and many thought that was the problem, but it was proven that wasn't the case. I can't remember exactly what the cause was but it was something along those lines.
apparently one of his closest friends suggested that the pressure of his fame and other things meant senna couldn't cope and so decided to take his life, i think thats bullshit, but it was a close friend who said that.
i personally really dont know. it happend in 94' i was only 11 years old, and only getting into the sport, but it will stay with me forever, watching was bad, they had blankets covering the scene so we couldnt see what was going on, murray wasnt talking much, so i knew it was serious, later tht day on the news he was pronounced dead, i was young but still felt the impact, the only other time i've felt like this was watching burti at spa, car burried in the tyres, and the blankets coming out, not good.
whatever really happened we might never know, but his legend will remain, thats the main thing.