'Tragedy' of Trayvon Martin

President Obama has said the death of Trayvon Martin is a tragedy that needs to be investigated immediately.

Speaking from the White House, he said America needs to do some "soul-searching" to discover how and why the unarmed teen was murdered.

Across Florida and America thousands have marched in to demand his killer be arrested.

Hundreds of so-called "hoodie marches" have been taking place on an ad-hoc basis as community leaders, students and celebrities protest against the police reaction.

17-year-old Trayvon Martin was an shot dead in Sanford, Floriday on February 26th by 28-year-old George Zimmerman.

Martin had been watching an NBA basketball game on TV a his father's girlfriend's house in a gated community when he left the house to walk to a nearby 7-Eleven.

On his way back from the shop he was spotted by George Zimmerman.

Zimmerman called the police to report "suspicious behaviour" in his area, he told police he was following the young man. The police told him this was not necessary, however he continued to do so.

When they turned up, Trayvon was dead, and Zimmerman was not arrested as he claimed he acted in self-defence.

Florida has a "stand your ground law" that allows someone in fear of "great bodily harm" to respond with deadly force. This controversial law is now being reviewed by a specially appointed state task force.

The family of Trayvon have been campaigning for his killer to be arrested for murder and have launched an online petition which has so far been signed by more than 1.5 million people.

As details of the 911 call emerged, a host of celebrities on twitter urged people to march, sign the petition and to join what has become an national movement for justice.

Today President Obama has called for a full investigation into the death. George Zimmerman has not been arrested.

Geraint Vincent reports from Washington.