Question: The man known for trying to prove the innocence of Sirhan Sirhan in the assassination of Robert F. Kennedy is also known for defending the man entered what type of plea in his trial for the assassination of Martin Luther King?

Context articles: James Earl Ray
Sirhan Sirhan
Gerald Posner
King Kennedy
Grant Cooper
William Francis Pepper
Lynn Compton
RFK (film)
Robert F. Kennedy's 1948 visit to Palestine
RFK Must Die

James Earl Ray (March 10, 1928 – April 23, 1998) was a convicted murderer who assassinated Martin Luther King Jr. on April 4, 1968 in Memphis, Tennessee.
 Ray was convicted on his 41st birthday after entering a guilty plea to forgo a jury trial.
 Had he been found guilty by jury trial, he would have been eligible for the death penalty.
Sirhan Sirhan (born سرحان بشارة سرحان , "Sirḥān Bishāra Sirḥān"; on March 19, 1944) is a Palestinian with Jordanian citizenship who assassinated Robert F. Kennedy on June 5, 1968.
 Sirhan was found guilty and is currently serving a life sentence at the Richard J. Donovan Correctional Facility in San Diego County, California.
Gerald Leo Posner (born May 20, 1954) is an American investigative journalist and author of twelve books, including "Case Closed: Lee Harvey Oswald and the Assassination of JFK" (1993), which explores the John F. Kennedy assassination, and "Killing the Dream: James Earl Ray and the Assassination of Martin Luther King, Jr." (1998), about the assassination of Martin Luther King, Jr. A plagiarism scandal involving his articles and books arose in 2010.
 In 2015, the "Chicago Tribune" called Posner "a merciless pitbull of an investigator."
King Kennedy is an upcoming drama thriller film set in the 1960s made entirely from archive material.
 The film stars some of the most prominent characters from 1960s America, including US President John F. Kennedy, Robert F. Kennedy, the civil rights movement leader Martin Luther King, convicted assassins Lee Harvey Oswald and Sirhan Sirhan and the film world's brightest icons of that time Marilyn Monroe and Frank Sinatra.
 The plot line revolves around the concepts of truth and freedom, but pursues further towards deception, intrigue, conspiracy and murder, and features some of the most memorable moments in 1960s America, including Marilyn Monroe's world-famous "Happy Birthday, Mr. President" at Madison Square Garden and Martin Luther King's "I Have A Dream" speech on the steps of the Lincoln Memorial in which he called for racial equality and an end to discrimination.
 The film is designed primarily to remind, focusing on the characters and events that build up to the assassinations of John F. Kennedy, Robert F. Kennedy and Martin Luther King as their apparent determination to shy away from war, discrimination and hatred became ever more publicized.
Grant B. Cooper (April 1, 1903, in New York City – May 3, 1990), was the chief defense attorney in the murder trial against Sirhan Sirhan for the assassination of Robert F. Kennedy.
 Sirhan's more recent counsel has accused Cooper of deliberately throwing the Sirhan case as the result of a then-pending indictment against Cooper for possessing stolen transcripts of the grand jury proceedings in the Beverly Hills Friar's Club card cheating case.
 Cooper, who faced the possibility of jail time, was eventually fined $1000.
 Cooper died in 1990 of an aortic aneurysm.
William Francis Pepper (born August 16, 1937) is an attorney based in New York City who is most noted for his efforts to prove government culpability and the innocence of James Earl Ray in the assassination of Martin Luther King, Jr. Dr. Pepper has also been trying to prove the innocence of Sirhan Sirhan in the assassination of Robert F. Kennedy.
 He is the author of several books.
 He has been active in other government conspiracy cases, including the 9/11 Truth movement, and has advocated that George W. Bush be charged with war crimes.
Lynn Davis "Buck" Compton (December 31, 1921 – February 25, 2012) was a California Court of Appeal judge who served as the lead prosecutor in Sirhan Sirhan's trial for the assassination of Robert F. Kennedy.
 From 1946 to 1951, he served with the Los Angeles Police Department.
 During World War II, he was a commissioned officer with E Company, 2nd Battalion, 506th Parachute Infantry Regiment, in the 101st Airborne Division of the United States Army.
 Compton was portrayed in the HBO miniseries "Band of Brothers" by Neal McDonough.
RFK is a 2002 American television film directed by Robert Dornhelm.
 It takes place through the eyes of Robert F. Kennedy after his brother John F. Kennedy's assassination in 1963.
 As he lives through the loss, he starts to identify himself as a political figure, not just the former President's brother.
 He makes it official with a Presidential bid in 1968 to what he says was to "save the Democratic Party."
 During his campaign, in which the American people showed great support for him, RFK was shot and killed by Sirhan Sirhan.
Robert F. Kennedy visited the British Mandate of Palestine in 1948, one month before Israel declared its independence.
 Twenty-two years old at the time, he was reporting on the tense situation in the region for "The Boston Post".
 During his stay, he grew to admire the Jewish inhabitants of the area.
 He later became a strong supporter of Israel; this was later cited as Sirhan Sirhan's motivation for assassinating him on the first anniversary of the start of the Six-Day War on June 5, 1968.
 Sirhan happened to see a documentary about Kennedy in Palestine in 1948.
 Later in his murder trial, Sirhan Sirhan testified: "I hoped he will win Presidency until that moment.
 But when I saw, heard, he was supporting Israel, sir, not in 1968, but he was supporting, it from all the way from its inception in 1948, sir..." Author Robert Blair Kaiser points out a discrepancy in the timing of Sirhan's decision.
 In Sirhan's diary, the entry in which he decided to kill Robert Kennedy was made on May 18.
 The documentary in question was first shown on TV in the Los Angeles area on May 20.
 When asked to explain, Sirhan said that he did not recall writing the journal.
RFK Must Die: The Assassination of Bobby Kennedy is an investigative documentary by Irish writer and filmmaker Shane O'Sullivan released in 2007.
 The film expands on his earlier reports for BBC "Newsnight" and "The Guardian" and explores alternative theories of what happened the night Robert F. Kennedy was shot at the Ambassador Hotel in Los Angeles on 5 June 1968.
 The title comes from a page of "free writing" found in assassin Sirhan Sirhan's notebook after the shooting, in which he wrote "R.F.K. must die - RFK must be killed Robert F. Kennedy must be assassinated... before June 5 '68."