A new play by the creator of Casualty is seeking to finally give a definitive answer to what happened on July 22, 2005, the day when Jean Charles de Menezes was shot by armed police at Stockwell tube station.

Paul Unwin could not get to work in central London that day and watched events unfold on his television, immediately thinking he wanted to make a film out of it but court cases and inquests since then meant he couldn't find a producer willing to back him.

A chance meeting with the artistic director of Theatre503 five months ago though led to Unwin pairing up with American writer Sarah Beck, and together they have sifted through mountains of research and interviews to put together what they believe is the closest thing to the truth there ever will be.

"We show why it happened and how it happened," says Unwin.

"The reason it is called This Much is True is because there is a lot of ambiguity of what is true and I think probably we have put it more clearly than anyone as to exactly what happened and why he got shot.

"I think I can put my hands up and say, for all the research we have done, the people we have spoken to and reading the very long inquest, we have a very clear sense of why the tragedy occurred.

"We interviewed people, met the family and spoke to senior cops, who when they realised we weren't out to bash the police but try and work out what the real significance of this horrible event was got very keen.

"What has then emerged is a play which really has voices never heard before and you get a very diverse sense of the experience of what happened.

"It's not a very anti-police play, it is about the tragedy, it's about how it unfolded and what went wrong.

"Most important is what happened in the four years afterwards "We spoke to people who said whenever they saw an Asian guy on the tube they might move into another courage and if they saw an Asian guy with a rucksack they would definitely move to another courage.

"On the other side we spoke to Asians that said whenever they carry a rucksack they are fearful of being shot by police."

On top of being the co-creator of Casualty and Holby City, Unwin was also nominated for an Oscar for his short film Syrup.

"That was an all time magic moment going to the Oscars," he says.

"My anecdote is that Tarantino was in the row across from us and I went over to say hello as we had chatted a fair bit the night before.

"He said, "you should meet Uma, this is Uma Thurman," and as this beautiful woman was coming down the steps my claim to fame is that I stepped backward and literally fell over.

"My Oscar moment was falling over."

This Much Is True, Theatre 503, The Latchmere, Battersea Park Road, October 27 to November 21, Tuesday to Saturday 7.45pm, Sundays 5pm, £13. Call 020 7978 7040 or visit theatre503.com.