Ayrton Senna on the floor, working with the Williams team

On the floor, working. Ayrton Senna was one of those drivers who, despite being millionaire, didn't mind to get on his knees and work hand in hand with his mechanics. His dedication to his craft was total, as Emerson Fittipaldi said about him 2 weeks ago.

Poster Grand Prix Brazil 1985 - Ayrton Senna's debut in the Lotus team

GP BRASIL 1985 Jacarepaguá RJ - ESPECIAL GP BRASIL 84/94

In this new season in Formula 1, the grid was significantly rendered to the wonders of the Turbo engine , which was already the dominant part in a time where new drivers and new teams assumed their presence in the top category of motor racing.

The McLaren team champion of the world , would keep the duo who gave them their first constructors' title since 1976 , the veteran Austrian driver Niki Lauda and the French Alain Prost. At 36 years old, Lauda was the driver with the number 1 on his car, but his teammate was becoming a name to be taken into account, and failed to win the title the past two years for very little, all knew that this was going to land on his lap sooner or later. Continuing with the MP4 / 2 model with TAG- Porsche engine, were on track .

But McLaren had rivals. To start with they had the Ferrari , which had kept the couple of the previous year, Italian Michele Alboreto and Frenchman René Arnoux, and a new engine, the 126/85 model, hoping it was able to overtake the cars of Lauda and Prost .

Another candidate was Williams. With the Honda engine, the team of Frank Williams and Patrick Head had expected things to be better than the previous year, which have adapted to the Turbo of Japanese origin. And they kept the Finn Keke Rosberg in their ranks, though now as a teammate he had the British Nigel Mansell, from Lotus .

In this team, with a Renault Turbo engine, Mansell 's replacement was the revelation  driver of the last season, driving for the Toleman : Brazilian Ayrton Senna. Although he was not at the top of his form, for he had spent much of the European winter recovering from a facial paralysis, it had  been enough to be ready to try the new machine at the first race of the year, moreover in his native Brazil. By his side , he had as teammate Italian Elio de Angelis, who raced the black and gold car for the sixth consecutive season .

Ayrton Senna and teammate Elio de Angelis, Lotus team, 1985

Investigation and trial on Ayrton Senna's accident at Imola 1994

The Williams team was entangled for many years in a court case with the Italian prosecutors over manslaughter charges, ending in a guilty verdict for Patrick Head. 

The Italian Court of Appeal, on April 13, 2007, stated the following in the verdict numbered 15050: “It has been determined that the accident was caused by a steering column failure. This failure was caused by badly designed and badly executed modifications. The responsibility of this falls on Patrick Head, culpable of omitted control”. Even being found responsible for Senna’s accident, Patrick Head wasn’t arrested: in Italy the statute of limitation for manslaughter is 7 years and 6 months, and the final verdict was pronounced 13 years after the accident.

A 600-page technical report was submitted by Bologna University under Professor of Engineering Enrico Lorenzini and his team of specialists. The report concluded that fatigue cracks had developed through 70% of the steering column at the point where it had broken. Lorenzini stated: “It had been badly welded together about a third of the way down and couldn’t stand the strain of the race. We discovered scratches on the crack in the steering rod. It seemed like the job had been done in a hurry but I can’t say how long before the race. Someone had tried to smooth over the join following the welding. I have never seen anything like it. I believe the rod was faulty and probably cracked even during the warm-up. Moments before the crash only a tiny piece was left connected and therefore the car didn’t respond in the bend.”

Senna did not like the position of the steering column relative to his seating position and had repeatedly asked for it to be changed. Patrick Head and Adrian Newey agreed to Senna’s request to lengthen the FW16′s steering column, but there was no time to manufacture a longer steering shaft. The existing shaft was instead cut, extended by inserting a smaller-diameter piece of tubing and welded together with reinforcing plates. Many surmise, based on the “yellow button tracking analysis” done in 1997 by CINECA that the movement of the steering wheel during the final seconds into Tamburello was abnormal. A reference point (yellow button) on the onboard video is seen to move several centimetres in its own plane, due to the steering wheel moving up and down, indicating a fully or partially buckled steering column.
Williams released its own video to prove the movement was normal by Coulthard manhandling an FW16B steering wheel, yet the effort required by Coulthard to deflect the wheel in the demonstration is termed to be “quite considerable”. The nature of Tamburello requiring a light and anticipatory grip on the wheel (because of the high speed and bumps) coupled with Senna’s slight frame causes some to question whether or not the movement of the yellow button was indeed as “normal” as Williams has claimed.

No known analysis has been done on the tracking of the yellow button at other laps of the FW16 around Imola or other racing circuits.

During the trials, Fabrizio Nosco, a Regional technical commissioner, testified that both of the vehicle’s black boxes were intact, except for minor scratches. He said “I have seen thousands of these devices and removed them for checks. The two boxes were intact, even though they had some scratches. The Williams device looked to have survived the crash.”. In a move that apparently breached FIA regulations, Charles Whiting, a FIA official, handed the black boxes to Williams before the regulating body’s own investigation into the accident. Williams claimed the black boxes were unreadable, and the boxes returned for the court proceedings were indeed unreadable, a full month after the accident. The black boxes might have put to rest the cause of the accident.

At the conclusion of the Italian trial, Senna’s FW16, chassis number 02, was returned to the Williams team. The team reported that the car was in an advanced state of deterioration and was subsequently destroyed. The car’s engine was returned to Renault, and its fate is unknown.

His death was considered by many of his Brazilian fans to be a national tragedy, and the Brazilian government declared three days of national mourning. Senna is buried at the Cemitério do Morumbi in his hometown of São Paulo.

Source: http://www.sennafiles.com/ayrton-senna/death/investigation-and-trial/

Was the Williams team legally found guilty for Senna's death?

Yes. But nobody paid in the end.

This is very little known but yes, the Williams team was finally found guilty for Senna's death. 
"The Williams team was entagled for many years in a court case with the Italian prosecutors over manslaughter charges, ending in a guilty verdict for Patrick Head. The Italian Court of Appeal, on April 13, 2007, stated the following in the verdict numbered 15050: "It has been determined that the accident was caused by a steering column failure. This failure was caused by badly designed and badly executed modifications. The responsibility of this falls on Patrick Head, culpable of omitted control". Even being found responsible for Senna's accident, Patrick Head wasn't arrested: in Italy the statute of limitation for manslaughter is 7 years and 6 months, and the final verdict was pronounced 13 years after the accident."

Ayrton Senna had the good looks of a romantic hero

Death, perhaps inevitably, has lent Ayrton Senna's legend a romanticised sheen. The greatness of the man and the brilliance of his driving are remembered easily, the occasional darkness of his psyche perhaps less so. But it does Senna a disservice to honour only part of his legacy. The significance of his achievements cannot be properly understood without a full appreciation of their origins.

Ayrton Senna facts

World champion three times
161 grand prix starts
41 wins
65 pole positions
First race - 1984 Brazilian GP
First win - 1985 Portugese GP
Last win - 1993 Australian GP
Last race - 1994 San Marino GP

He had the good looks of a romantic hero, a charisma that could quieten any room, the eloquence of a poet and a spirituality with which millions felt they could identify. His dark eyes were windows to a soul of complexity and volatility. All that made him into a demi-god in his homeland of Brazil, and admired the world over like few sportsmen before or since.

But with that determination, and his own knowledge of just how good he was, came a sense of entitlement that was less attractive and which led him to take actions that put his own life - and the lives of his opponents - at risk.