An Act of State: the execution of Martin Luther King by William F Pepper

The attorney William Pepper has spent a quarter of a century investigating the assassination of Martin Luther King, sifting through evidence, interviewing witnesses, gradually piecing together the accumulated jigsaw. He concluded that King's murder in Memphis in 1968 was the result of a conspiracy involving local, state and federal agencies.

At a civil trial in 1999, at which he represented the King family, Pepper at last presented what he had learned to a jury – the first and, so far, only jury to examine this crime. After hearing 70 witnesses, the jury agreed with Pepper and the King family: the prophet of freedom whose birthday is honoured as a national holiday was executed by his own government.

Because it was a civil hearing, Pepper was required only to prove that the conspirators were guilty on the balance of probabilities, not beyond a reasonable doubt. Given the murky historical residue, we're unlikely ever to secure a higher degree of certainty. But few who read Pepper's book will not concur that it is more than sufficient to cause alarm and outrage.

The evidence of Memphis Police Department involvement seems conclusive, and if the case for the involvement of military intelligence is not as strong, it is still too substantial to be dismissed. In Pepper's account, organised crime acted as the front-line facilitator of the hit. Again, the evidence seems solid.

Pepper is all too aware that parallels with the assassination of John F Kennedy may damage his credibility (he chose not to put before the jury indications he had uncovered of links between the two traumatic killings). Aware that conspiracy theorists are mistrusted, he also eschews Oliver Stone-style dramatics, and opts instead for detail and thoroughness.

It is often argued that conspiracies of this magnitude are inherently implausible because so many people would have to keep the secret. In this case, the logic of plausibility works the other way. For there not to have been a conspiracy – for the official lone gunman explanation to be true – would imply that a large number of unrelated individuals had fabricated evidence to the contrary. That is essentially the claim of the US Justice Department in its rebuttal of the civil findings.

Establishing a motive for the conspirators is the easy part. In 1968, the US was gripped by unrest. There were many individuals scattered across the sprawling state apparatus convinced that King posed a revolutionary threat (J Edgar Hoover among them). Some, it appears, decided to do something about it.

It's impossible to know what King would have become had he lived, but hard to believe that – at this moment – he would be anything other than an outspoken opponent of President Bush's war policy. Whatever the American establishment's role in his death, since then it has worked hard to tame his legacy, and with much success. They have reduced this mass agitator to an innocuous icon of brotherly love. The lone gunman theory comes in handy here. It helps to obfuscate the reality that at the time of his death, King was hated and feared by the bulk of white America, and was persecuted by its organs of government.