Doreen Lawrence, mother of murdered teenager Stephen Lawrence, speaks to journalists after Gary Dobson and David Norris were sentenced in his killing at the Old Bailey, the Central Criminal Court in London. (Luke MacGregor/Reuters)

A judge sentenced two white men to life in prison on Wednesday for killing a black teenager more than 18 years ago, a case that exposed racism in Scotland Yard and prompted widespread soul-searching about race relations in Britain.

Gary Dobson, 36, and David Norris, 35, were found guilty of murder after a six-week trial triggered by new forensic evidence. Dobson will serve a minimum of 15 years and two months, and Norris will serve at least 14 years and three months.

The “evil” crime was committed for “no other reason than racial hatred,” Judge Colman Treacy told a packed courtroom Wednesday at the Old Bailey, London’s Central Criminal Court.

In April 1993, Stephen Lawrence, 18, was waiting at a bus stop in southeast London when five or six men swarmed around him and began shouting racist abuse. He was stabbed to death for no other apparent reason than his race.

Britons were shocked at the crime and later at the handling of the case. Critics questioned why it took the police more than two weeks to make any arrests, even though the names of suspects, including Dobson and Norris, were given to them within days of the killing. A photographer watching two of the key suspects reportedly saw them haul away clothes in plastic bags, which were never found.

An official inquiry later accused the police of systemic racism, which resulted in the bungling of the case.

“It looked as though, in Britain in the late 20th century, you could kill a black man for fun and get away with it. No wonder that no case before or since so alienated and discouraged Britain’s ethnic minorities,” the Times of London said in an editorial on Wednesday.

The Lawrence case was a “Rosa Parks moment,” said Matthew Ryder, a lawyer who previously worked for the Lawrence family. He said the police’s bungling of the investigation pricked a nation’s conscience and opened a more sophisticated discussion about racism in Britain — not just among ethnic minorities, but among whites as well.

The case led to the “condemning of racism not just in its crude forms, but in its subtle forms. It began a discussion about racism which was much more modern,” Ryder said.

Several suspects were later arrested in the killing, but the state concluded that there was insufficient evidence to prosecute them. Undeterred, the Lawrence family took the unusual step of launching its own private prosecution of three suspects, including Dobson, but the case collapsed in court.

A 1999 government-commissioned inquiry into the London Metropolitan Police’s initial investigation accused the police of incompetence, poor leadership and “institutional racism,” a term that became inexorably linked to the case.

The inquiry’s findings, known here simply as the Macpherson report, recommended 70 measures, many aimed at tackling racism in the police and other institutions. One of the recommendations urged British lawmakers to scrap an 800-year-old “double jeopardy” law that prevented someone from being tried twice for the same crime, even if new evidence came to light. This proved critical in pursuing a new case against Dobson.

For its part, Scotland Yard hired more ethnic minority officers and overhauled the ways it investigates race-related crimes and deals with relatives of victims.

But many say tremendous challenges remain. For instance, Brian Paddick, a former senior officer at the Metropolitan Police, told the BBC on Wednesday that the police in London need to address the “unacceptable” fact that black people are five times more likely to be stopped and searched than white people.

In 2006, Scotland Yard ordered a cold-case review of the evidence in Lawrence’s killing. Using technology unavailable at the time of the murder, the police discovered tiny specks of Lawrence’s blood on Dobson’s bomber jacket, and hairs and fibers from Lawrence on Norris’s jeans and sweater. The defense argued that the evidence had been contaminated after years of mishandling by authorities.

Before declaring Dobson and Norris guilty on Tuesday, the jurors asked to again see footage covertly filmed by police, who had installed a secret camera in Dobson’s apartment a year after Lawrence’s murder. In one eerie passage, Norris says he would skin a black person alive and set him on fire.

During the sentencing, the judge was forced to take into account that Dobson was 17 and Norris was 16 at the time of the murder.

Speaking outside the Old Bailey court in London, Lawrence’s mother, Doreen, said that the sentences were “quite low” but that she understood the judge’s hands were tied.

“It’s the beginning of starting a new life,” she said.