Why was the death of Ayrton Senna so controversial? [References]

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Ayrton Senna - The Senna Files, 1996. The Mystery Continues. [Online]
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Available at: http://www.bbc.co.uk/sport/0/formula1/24358508

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charrotest, 2009. The death of Ayrton Senna - what Natgeo did not say. [Online]
Part One Available at: https://www.youtube.com/watch?v=ayjOW5DnwgM
Part Two Available at: https://www.youtube.com/watch?v=HM6MzcdK62k
Part Three Available at: https://www.youtube.com/watch?v=CX2Sd_Ww-HA
Part Four Available at: https://www.youtube.com/watch?v=2f9pumnvqDI
Part Five Available at: https://www.youtube.com/watch?v=1NjSIZfG5rk

ESPN, 2010. Ayrton Senna: In his own words. [Online]
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Williams, R., 2010. The Death of Ayrton Senna. 3rd ed. s.l.:Penguin .

Казаков, О., 2013. F1 San-Marino 1994 Crash Ayrton Senna. [Online]
Available at: https://www.youtube.com/watch?v=PMNnDiVohn0

Sources also consulted without explicit Reference:

Ayrton Senna, 2008. Death of Ayrton Senna: How the crash happened [Online]
Available at: https://www.youtube.com/watch?v=k2_2S3v07Bs

Benson, A., 2013. Ayrton Senna's death still haunts designer Adrian Newey. [Online]
Available at: http://www.bbc.co.uk/sport/0/formula1/24358508

Channel 4 News, 2011. Ayrton Senna: Would he have survived a crash today? [Online]
Available at: http://www.channel4.com/news/ayrton-senna-would-he-have-survived-a-crash-today

F1 Technical, 2008. Ayrton Senna Murdered [Online]
Available at: http://www.f1technical.net/forum/viewtopic.php?t=5573

Wikipedia, 2014. 1994 San Marino Grand Prix [Online]
Available at: http://en.wikipedia.org/wiki/1994_San_Marino_Grand_Prix

Wikipedia, 2014. The Death of Ayrton Senna [Online]
Available at: http://en.wikipedia.org/wiki/Death_of_Ayrton_Senna

Yahoo Answers, 2006. What exactly happened in the 1994 death of Ayrton Senna? [Online]
Available at: https://answers.yahoo.com/question/index?qid=20060928150245AAPgdiA

Shaun Parker, NO DATE. Controversy Surrounding the Death of Ayrton Senna [Online]
Available at: http://www.streetdirectory.com/travel_guide/50508/car_accidents/controversy_surrounding_the_death_of_ayrton_senna.html

Wikipedia, 2014. Roland Ratzenberger [Online]
Available at: http://en.wikipedia.org/wiki/Roland_Ratzenberger#Death

Matt Hill, 2010. The 1994 Senna Disaster: The Day Formula 1 Lost Its Remaining Innocence [Online]
Available at: http://bleacherreport.com/articles/516260-the-1994-senna-disaster-the-day-formula-1-lost-its-remaining-innocence

Andy Hallbery, 2011. San Marino Grand Prix, Imola 1994 – The worst weekend [Online]
Part One available at: http://www.motorsportretro.com/2011/06/imola-1994/
Part Two available at: http://www.motorsportretro.com/2011/06/san-marino1994/
Part Three available at: http://www.motorsportretro.com/2011/06/ayrton-senna-1994/
Part Four available at: http://www.motorsportretro.com/2011/06/ayrton-senna-death/