Adrian Newey, the man who designed the cars that have made Red Bull a dominant force in Formula One, has spoken for the first time about how close he came to leaving the sport after the 1994 death of Ayrton Senna in one of his cars.

In a wide-ranging interview with the Guardian, Newey revealed how badly he was affected when Senna was killed while leading the San Marino Grand Prix in a Williams car.

"The little hair I had all fell out in the aftermath," Newey said. "So it changed me physically. It was dreadful. Both Patrick Head [Williams's technical director] and myself separately asked ourselves whether we wanted to continue in racing. Did we want to be involved in a sport where people can die in something we've created? Secondly, was the accident caused by something that broke through poor or negligent design? And then the court case started."

Newey and Head were charged with manslaughter in Italy – but his soul-searching was the reason he considered leaving Formula One. "The court case was a depressing annoyance, and extra pressure, but it did not make me question whether I wanted to be involved in F1. It's the self-searching rather than the accusations that really matter."

Asked if he came close to walking away permanently, Newey replied: "Yes. For the whole team it was incredibly difficult. I remember the day after the race was a bank holiday Monday and some of us came in to try and trawl though the data and work out what happened. They were dark weeks. The honest truth is that no one will ever know exactly what happened. There's no doubt the steering column failed and the big question was whether it failed in the accident or did it cause the accident? It had fatigue cracks and would have failed at some point. There is no question that its design was very poor. However, all the evidence suggests the car did not go off the track as a result of steering column failure."

Newey admits that he has considered the causes of the crash repeatedly over the past 17 years. "If you look at the camera shots, especially from Michael Schumacher's following car, the car didn't understeer off the track. It oversteered which is not consistent with a steering column failure. The rear of the car stepped out and all the data suggests that happened. Ayrton then corrected that by going to 50% throttle which would be consistent with trying to reduce the rear stepping out and then, half-a-second later, he went hard on the brakes. The question then is why did the rear step out? The car bottomed much harder on that second lap which again appears to be unusual because the tyre pressure should have come up by then – which leaves you expecting that the right rear tyre probably picked up a puncture from debris on the track. If I was pushed into picking out a single most likely cause that would be it."

His cars have won 119 races, seven constructors' titles and six drivers' championships, but Newey admits that Senna's death still haunts him. Asked if he has seen the acclaimed documentary, Senna, the 52-year-old said: "No. It would not be an easy thing to do."