A 71-year-old man alleged to have been a member of the Ku Klux Klan has been found guilty of kidnapping and conspiracy in the 1964 deaths of two black teenagers that sparked a summer of violence later depicted in the film Mississippi Burning.

James Ford Seale had pleaded not guilty to the charges relating to the deaths of Charles Moore and Henry Dee, both aged 19 at the time of their disappearance on May 2 1964. Their bodies were later found in the Mississippi river.

Seale's conviction was achieved on the words of a confessed Klansman, Charles Edwards, who was granted immunity from prosecution in exchange for turning on his old friend.

He testified that Seale had belonged to the same Klan chapter, or klavern, as he had, which was led by Seale's late father. The prosecution team admitted to the jury they had made "a deal with the devil" but argued that it was the only way to get justice 43 years after the killings.

Seale, who declined to testify, now faces up to two life sentences. He is unlikely to leave prison alive.

As the guilty verdicts were returned, the victims' relatives hugged each other and cried.

Seale's prosecution may mark one of, if not the last trial of its kind from the brutal heyday of the KKK and its violent clashes with the civil rights movement. As witnesses pass away, the likelihood of further trials diminishes.

During the trial, the jury heard that white supremacists, often with the complicity of local police officers and the courts, were consciously targeting civil rights activists in an attempt to terrorise them into silence. Seale was arrested a few months after the men disappeared, but murder charges were later dropped against him.

Prosecutors alleged that the two victims had been picked up while they were hitchhiking, thrown into the boot of a car and taken to a forest where they were beaten in an attempt to extract information on firearms being brought into the area.

Edwards said that he saw Seale hold a gun to Dee and Moore, while the two young black men were beaten for about half an hour, 30 or 40 times each. Edwards claimed that although he had been involved in the beating, he had not been present when the men had been thrown into the river.

He said Seale later told him how the men were dumped alive in a backwater of the Mississippi river with weights attached to them.

Defence lawyers that the case was flimsy because it relied on the evidence of one man, an "admitted liar". "This case all comes down to the word of one man, an admitted liar, a man out to save his own skin. A case based on his word is no case at all," the lead defence lawyer, Kathy Nester, said.

Seale has always denied membership of the KKK.

Before the trial started, a former FBI agent gave evidence that he had confronted Seale and accused him of the murder a few months after the deaths. Edward Putz said Seale had replied: "Yes, but I'm not going to admit it. You are going to have to prove it."