What you need to know about the assassination of Martin Luther King Jr.

Over a half-century ago, Martin Luther King Jr. traveled to Memphis to support and bring attention to a strike by more than 1,300 city sanitation workers, but the journey to Tennessee would cost him his life.

Fifty-one years have passed since one of the nation's most harrowing episodes unfolded, when at 6:05 p.m. an assassin named James Earl Ray took aim with a Remington .30-06 rifle and squeezed off a single shot that changed the trajectory of the civil rights movement.

Why was King in Memphis?

On Feb. 1, 1968, Memphis garbage collectors Robert Walker and Echol Cole were crushed to death when a garbage truck malfunctioned. The incident cast a light on the poor working conditions and low wages of sanitation workers, who were prompted by the deaths of the two men to call for a strike.

Sanitation workers, all of them black, walked off their jobs on Feb. 12 and set up picket lines, toting signs reading, "I Am a Man."

King, a Baptist minister from Atlanta and the country's most famous civil rights activist, had heard about the work stoppage and decided to go to Memphis to bring national attention to the strike. He had already come to national prominence by leading the bus boycott in Montgomery, Alabama, in 1955, after an African-American woman named Rosa Parks was arrested for refusing to give up a front bus seat to a white man.

Martin Luther King Jr.: A life in pictures

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Martin Luther King Jr. was a Baptist minister and civil rights activist who helped lead the fight for racial equality in the United States. His most famous work is his “I Have a Dream” speech in which he spoke of his dream of a United States that is without segregation or racism. King led many marches and protests, including the Montgomery bus boycott and some of the Selma-to-Montgomery marches in Alabama. In 1964, King won the Nobel Peace Prize for combating racial inequality through nonviolent resistance. He was assassinated in Memphis, Tennessee, on April 4, 1968.King circa 1964.

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In the decade following the boycott, King became a civil rights rock star organizing non-violent protests for racial and economic equality. In 1963, he organized a massive march on Washington to demand change, and gave a blistering speech on the National Mall, calling out the federal government for its "apathy and hypocrisy, its betrayal of the cause of justice."

"I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character," King told the crowd.

By the time he went to Memphis, King had been awarded the 1965 Nobel Peace Prize.

Why did King stay at the Lorraine Motel in Memphis?

King and his entourage checked into the Lorraine Motel on April 3, 1968. The Lorraine was one of the few motels in Memphis that was known as friendly to African Americans.

Within hours after checking into Room 306 at the Lorraine, King, battling a bad cold, spoke to an overflow crowd at the Mason Temple Church. Many in the audience were striking sanitation workers. King gave his famous "Mountain Top" speech, in which he spoke of his own mortality, telling the crowd, "I've seen the Promised Land. I may not get there with you. But I want you to know tonight, that we, as a people, will get to the Promised Land."

Where was King going when he was killed?

The next day, April 4, King and his inner circle had been invited to have dinner at the home of the Rev. Samuel Billy Kyles, a Memphis minister. About 6 p.m., King, dressed in his trademark dark suit and tie, emerged from Room 306.

Andrew Young, his close friend and partner in the civil rights movement, yelled up to him to grab his coat because the weather had turned chilly. Before he could answer Young, a shot rang out.

A bullet hit King in the right cheek, shattering his jaw, several vertebrae and severing his spinal cord. He was rushed to St. Joseph's Hospital, where he was pronounced dead at 7:05 p.m.

What happened in the aftermath of King's death?

Word of King's assassination triggered riots in more than 100 cities across the country, including Chicago and Washington, D.C. More than 35 people were killed in the violence.

President Lyndon Johnson, who signed the Civil Rights Act in 1964 after being prompted to act by the movement King spearheaded, designated April 7, 1968, as a national day of mourning. The following day, King's widow, Coretta Scott King, went to Memphis and led the striking sanitation workers in a peaceful march.

On April 8, a funeral for King was held at the Ebenezer Baptist Church in Atlanta. Among those in attendance was former first lady Jacqueline Kennedy and Vice President Hubert Humphrey. Tens of thousands of mourners lined the streets of Atlanta to watch King's casket being carried by two mules to Morehouse College, King's alma mater, for a public memorial service.

A week later, the Memphis sanitation strike ended when the city council agreed to boost the workers' wages and improve working conditions.

When was King's assassin caught?

Ray, a 40-year-old convicted robber and prison escapee, was identified as King's killer after his fingerprint was found on the rifle used in the assassination and discarded near the murder scene. Police believe Ray shot King from a boarding house across from the Lorraine Motel, after stalking the civil rights leader for more than two weeks.

He was arrested in London on June 8, 1968, and extradited back to the United States to face prosecution.

In March 1969, Ray pleaded guilty in a Memphis courtroom to King's murder to avoid the death penalty. He was sentenced to 99 years in prison. He died from kidney disease on April 23, 1998, at the age of 70.