The parents of the murdered black American teenager Trayvon Martin have come to Britain to meet the family of Stephen Lawrence, and visit the spot where he was murdered in 1993.

Trayvon Martin's parents

The parents of 17 year old Trayvon Martin arrived in London this morning, to thank the British people who have lent their support.

Among the many letters of condolence which they received was one from Doreen Lawrence, whose own son was killed in a racist attack in South London 19 years ago. The two families met today, at the memorial to Stephen's death, united by a search for meaning, amid their personal grief.

A day to look back, as well as forward: a reminder of a young man's killing that has become as totemic for America as Stephen Lawrence's death was in Britain.

Trayvon's story

For the Martins, their grief is still raw: it's been barely two months since the night when their son walked through a gated community in Sanford, Florida and was challenged by neighbourhood watch volunteer George Zimmerman. There was a confrontation. Screaming. Gunshots. By 7.25pm, Trayvon Martin, armed only with a packet of Skittles and a soft drink, was killed.

The initial police investigation was so cursory, that Zimmerman was barely asked any questions about the shooting, his alleged injuries barely examined, charges never brought. Police said there was no evidence to disprove his claim that he shot Martin in self-defence.

Amid the growing backlash, and the growing distress of the black community, hundreds of thousands of people began signing an online petition demanding Zimmerman's arrest. Tapes of the 911 calls made on the night of the shooting emerged in the media. Finally the Justice Department launched its own investigation.

If I had a son, he would look like Trayvon. President Barack Obama

Barely a month after the shooting, Trayvon Martin had become a cause: a symbol not just of America's dysfunctional relationship with race, and guns, but a powerful political statement. "I am Trayvon Martin" became a nationwide slogan, emblazoned on banners, T-shirts, bumper stickers.

Thousands of people took to the streets, holding rallies around the country to demand "Justice for Trayvon". They wore hoodies, in tribute to the one the teenager was wearing the night he was shot: some brandished bags of Skittles. President Obama spoke publicly for the first time, calling for some national soul searching: "If I had a son, he would look like Trayvon", he said.

The hoodie swiftly became a symbol in itself, worn by members of Congress, sporting stars, school kids. The rallies became known as the 'Million Hoodie March'.

The Zimmerman family launched their own publicity effort too, with a series of television interviews giving their version of what happened. Zimmerman himself, who was in hiding, set up a website, asking for donations to help with his legal expenses.

Focus on guns

Soon, the focus became not simply race, but America's relationship with guns, and Florida's controversial "Stand Your Ground" law which allowed people to use deadly force to defend themselves if they felt a reasonable fear of death. 24 states have similar laws on their books.

Weeks after the fatal shooting, and the wounds are just as raw. Zimmerman is now on trial, charged with second degree murder: Sanford's new interim police chief has promised to reach out to those in the community who feel ignored by the authorities, along with an "A-Z review". Trayvon's parents continue their campaign for justice. Stand Your Ground laws and racial profiling rules are under the spotlight.

And America? America is just as divided: by race, by class, by generation.

Soul-searching

What the shooting has achieved is a more meaningful national conversation about race, some of that soul-searching which Obama called for back in March. For anyone who thought the election of a Black American to the highest office in the land meant some kind of milestone in the fight against racism, a nasty wake-up call. As Newsweek put it: "Despite the powerful symbolism of Obama's election, blacks and whites are still living in different worlds".

So: back to those fault lines, which have shattered through the veneer of America's supposedly tolerant modernity. 23 year old Rachel Hislop, on the Daily Grind, writes that she had sat silently while white colleagues questioned whether racism still existed in their "post-racial", privileged world. "But then a young black man called Trayvon Martin was killed, and the dirty blanket was finally pulled off the taboo conversation of the very present demon that is race relations in America, and I've decided I am tired of staying quiet", she wrote.

A nation divided

According to polls, twice as many blacks and Hispanics think race played a major part in the shooting, as whites: 73% compared to 36%. Black Americans paid much closer attention to news about the incident, overwhelmingly saw George Zimmerman guilty of a crime, and believe he would have been arrested far more quickly had the victim been white.

Trayvon Martin was killed by a stereotype. George Zimmerman is just the guy who fired the gun. Leonard Pitts Jnr

In the New Yorker, Jelani Cobb wrote that Trayvon's death "did not so much raise questions as it confirmed suspicions: that we remain stratified or at best striated by race, that innocent is a relative term, that black male lives can end under capricious circumstances, and that justice is in the eye of the beholder - ideas that are as cynical as they are applicable."

For the Pulizter prize winning commentator Leonard Pitts Jnr, it was never as simple as black victim, white perpetrator: at least some black men, he said, would have acted exactly the same as the neighbourhood watch volunteer. "To make this about Zimmerman is to absolve the rest of us for maintaining a society that, in ways both overt and covert, still makes criminality a function of skin. Trayvon Martin was killed by a stereotype. George Zimmerman is just the guy who fired the gun."

Today in London, then, two families whose lives have been fractured by loss will meet to mourn the loss of their sons. Personal tragedies, vastly magnified into political symbols, begging the most fundamental questions of our time. The nature of innocence, of justice, and of fair treatment: of the struggle to overcome generations of racism, suspicion, and mistrust.

A chance to make some sense, then, out of otherwise senseless deaths. Perhaps that the civility of great nations is not a lost cause, after all.

Felicity Spector writes about US affairs for Channel 4 News