"Martin Luther King himself became more and more concerned about problems untouched by civil rights laws-problems coming out of poverty. In the spring of 1968, he began speaking out, against the advice of some Negro leaders who feared losing friends in Washington, against the war in Vietnam…
King now became a chief target of the FBI, which tapped his private phone conversations, sent him fake letters, threatened him, blackmailed him, and even suggested once in an anonymous letter that he commit suicide. FBI internal memos discussed finding a black leader to replace King. As a Senate report on the FBI said in 1976, the FBI tried “to destroy Dr. Martin Luther King."
- Howard Zinn, “Or Does it Explode?” A People’s History of the United States.
No assassin was ever conclusively caught. James Earl Ray, the man who went to prison for the assassination, fought the rest of his life for a retrial, at the end with the support of the King family. Whether or not the government was involved in his assassination, it is clear that as soon as King shifted his focus from civil rights to poverty, he was considered an enemy of the state.
"… it’s inevitable that we’ve got to bring out the question of the tragic mix-up in priorities. We are spending all of this money for death and destruction, and not nearly enough money for life and constructive development… when the guns of war become a national obsession, social needs inevitably suffer."
- Martin Luther King, Jr, Spring 1968. King began to realize that civil rights laws could only do so much. The true threat to black oppression was the systemic poverty that the Civil Rights laws recently passed would have no effect on. Friends close to him advised against speaking out against it since he would lose allies in Washington. He was assassinated by an unknown marksman on April 6th.
"The provisions of this section shall not apply to acts or omissions on the part of law enforcement officers, members of the National Guard … or members of the Armed Forces of the United States, who are engaged in suppressing a riot or civil disturbance…."
- United States, Civil Rights Act, 1968. It also defined a riot as three or more people involving threats of violence.