'I used to hear them talking about the lynchings,' said Holmes, 79, who spent her childhood in the area, Prince George's County, Maryland.

Stephen Williams, a black man accused of manhandling a white woman, was beaten and hanged on the bridge in the early hours of 20 October, 1894. A masked mob snatched him from his cell and dragged him away as he pleaded for his life.

'When the Marlboro bridge was reached, the rope was quickly tied to the railing and amid piteous groans Williams was hurled into eternity,' the Washington Post reported.

There was no federal law against lynching and most states refused to prosecute whites for killing black people. The House of Representatives three times agreed to make lynching a federal offence. Each time, the measure died in the Senate at the hands of southern members.

Tomorrow, too late for Williams and the 4,742 others murdered by lynch mobs between 1882 and 1968, the Senate will vote on a motion apologising for the failure to enact an anti-lynching law first proposed 105 years ago.

'The apology is long overdue,' said Republican Senator George Allen, sponsoring the resolution with Democrat Mary Landrieu.

The action comes amid a flurry of reopenings of civil rights era cases. According to the Southern Poverty Law Centre in Alabama, 25 of them have been re-examined or are under re-examination. This has led to 26 arrests, 21 convictions, two acquittals and a mistrial.

Tomorrow, Edgar Ray Killen will go on trial for the murder of three young civil rights workers, the case that formed the basis for the film Mississippi Burning.

This month the body of 14-year-old Emmett Till was exhumed as part of an attempt to prosecute the handful of men still alive who may have been involved in his murder in Mississippi in 1955.

Till's death was a hugely galvanising event for the civil rights movement. Just three months after his death, when Rosa Parks famously refused to give up her seat on an Alabama bus, sparking the bus boycott that would kick-start the civil rights era, Emmett was on her mind.

In 1955, Roy Bryant and his half-brother, JW Milam, admitted in a magazine article they had killed Emmett - his 'crime' was to whistle at Roy's wife Carolyn in a drugstore. Their confession came two months after both men had been acquitted by an all-white, male jury who took 67 minutes to return the verdict.

Landrieu and other senators decided to back the bill after seeing the book Without Sanctuary: Lynching Photography in America, a collection of postcards taken at lynchings.

Towns across America bear reminders of the shameful tradition. In Alexandria, a lamp-post served to lynch Joseph McCoy on 23 April, 1897. In Annapolis, a bluff near College Creek was the site of Henry Davis's lynching just before Christmas in 1906.

Many African American families can name an ancestor or friend who fell to mob justice. Fred Tutman of Upper Marlboro can point to a tree on his family's land that a previous owner used for lynching.

'The memories are less vivid for me because of my generation,' said Tutman, 47. 'They are more vivid for my mother and grandmother, who had all kinds of violence perpetrated on them.'

Lynching touched all races and religions. Immigrants were frequent targets, so much so that at the start of the 20th century the State Department paid nearly $500,000 to China, Italy and Mexico on behalf of lynching victims.

But the killings were mainly in the South and four out of five victims were black, according to statistics compiled by Tuskegee University in Alabama. Many had not been accused of anything more than answering back a white man or looking at a white woman. Black landowners were frequent targets.

Before they were shot or hanged, some victims had their eyes gouged out or their teeth pulled with pliers, beaten, burned at the stake, dismembered or castrated.

'It was truly the American holocaust,' said Mark Planning, counsel for the Committee for a Formal Apology. 'There are perceptions that lynchings were carried out on some poor souls who were dragged into the woods. But these were public spectacles.'

Mob killings were often carnival-like events. Refreshments were sold, trains made special trips to lynching sites, schools and businesses closed to let people attend. Newspapers ran adverts for them. Corpses were displayed for days. Victims' ears, fingers and toes became souvenirs.

'Lynching was the socially acceptable way to demonstrate control,' said Lawrence Guyot, 66, a civil rights activist. 'It sent a message that not only did this happen to this person, but if you as a black person thought about stepping outside our racial code, it can happen to you. We want everybody to see it. We want the body to stay up as long as possible and all the gory details to be known.'

Seven Presidents argued for making it a federal offence. None of this swayed the Senate, where southerners insisted a federal law would intrude on states' rights.

The current effort was born out of a broader movement to ask Congress to acknowledge wrongs toward African Americans, including slavery. Support finally arrived for campaigners when the Committee for a Formal Apology sent copies of Without Sanctuary to senators.

One postcard, depicting a corpse in 1910, read: 'This is a token of a great day we had in Dallas 3 March.' Another, showing the burnt corpse of William Stanley in Temple, Texas, in 1915, read: 'This is the barbecue we had last night ... your son Joe.'