The twilight was growing on an unusually warm Memphis day April 4, 1968, when the shot rang out just after 6 p.m.

A single bullet, fired from a Remington 760 Gamemaster hunting rifle, screamed through the waning sunlight and killed the Rev. Martin Luther King Jr. at the age of 39.

“He never knew what hit him,” the Rev. Jesse Jackson, who was standing next to King when he was assassinated, told NBC last month.

“When you see something like that, you never really recover from such a scene.”

By the time of his death, King had already become a civil-rights icon, despite FBI Director J. Edgar Hoover’s proclaiming him “the most dangerous Negro of the future in this Nation.”

He caught the ear of President John F. Kennedy in 1963 with his famous “I Have a Dream” speech, helping prompt the president to call for the Civil Rights Act, which passed in 1964.

King had been awarded the Nobel Peace Prize in 1964 for his efforts.

He led thousands of protestors to the steps of Alabama’s statehouse as part of a voting-rights campaign just months before the passage of the Voting Rights Act of 1965, which bars racial discrimination at the polls.

The pastor and luminary was in Memphis on his Poor People’s Campaign — an effort to unite low-income people to demand better homes, jobs and education — when escaped convict James Earl Ray shot him April 4, 1968.

King had been in Tennessee for two days when Ray shot him as he stood on a second-story balcony at the Lorraine Motel.

About a week earlier, King had to cut short a junket to Tennessee, because riots and looting broke out at a march he was leading there.

But those riots couldn’t compare to the unrest that ensued in more than 100 US cities after King’s murder.

In New York, unrest erupted in Harlem and Bed-Stuy the night of King’s death, later spreading to Fordham and Brownsville.

“If that great man were alive today, there would be no question as to the importance of non-violent peaceful progress toward integration, rehabilitation and an open society,” then-Mayor John Lindsay said April 5, after touring Harlem the previous night to try and staunch the unrest.

There were nearly 400 arrests in four days, according to newspaper accounts at the time.

But unrest caused by King’s assassination also helped usher in both the Civil Rights Act of 1968 and the Gun Control Act of 1968.

President Lyndon Johnson urged Congress April 5 to pass the civil-rights legislation, citing riots over King’s death, according to the US Department of Housing and Urban Development. By April 11, it was law.

Months later, Johnson would sign the Gun Control Act, which was enacted in part as a response to King’s assassination.

With Wires