Robert Hathaway, an assistant forensics examiner for Rhode Island, said new technology could prove another rifle fired the shot that killed King on the balcony of the Lorraine Motel in April 1968.

That technology is a scanning electron microscope, which Hathaway said wasn't available until the mid 1980s.

``Knowing that the magnification is much greater and better it is an additional tool that can be used to possibly resolve the conflict over whether it was fired from this gun,'' said Hathaway, who spent 17 years in the crime lab for the Connecticut State Police.

Hathaway said the FBI used technology available at the time to test the bullet and rifle, but there has been ``no matching of the death slug to the rifle itself.''

The U.S. House Select Committee on Assassinations had the King rifle tested in the 1970s, but because the slug was so mangled, could not establish beyond a scientific doubt that it was the murder weapon.

Tests showed, however, that King was killed by the same kind of gun and that lead in the death slug matched unspent bullets found with the rifle.

Hathaway proposed a committee of three firearms experts fire test shots from the weapon and compare those with the bullet in evidence.

Ray's attorney, William Pepper, said he expects the tests on the rifle ``to exclude it for all time as the murder weapon.''

The 30.06 Remington rifle was found a few hundred feet from the motel where King was cut down by an assassin. It had Ray's fingerprints on it, and Ray pleaded guilty to killing King. He admitted buying the rifle and bringing it to Memphis.

He never stood trial because of his plea, but Pepper told the judge today: ``We are here to try to open that door through the presence of new scientific evidence.''

Before the hearing, prosecutors had said Ray has used up his appeals in Tennessee courts.

``He's the confessed killer. Nothing else out there can really be looked upon as credible evidence,'' said John Campbell, a state prosecutor.

State and federal courts have upheld Ray's guilty plea seven times.

Conspiracy theorists have argued for years that Ray, a bungling, petty criminal, could not have pulled off the assassination alone. And their theories, some of which include allegations of government wrongdoing, often note that authorities have never proven that Ray's gun was the murder weapon.

To have new tests, Ray's lawyers must first convince the courts that improved technology can determine if the rifle found at the scene killed King. They would then have to show that test results in Ray's favor help prove his innocence.

Having a guilty plea overturned on a claim of innocence is difficult, since the law assumes a person knows if he's guilty or not at the time the plea is given.

Usually, when a court throws out a guilty plea it's because it was coerced or a defendant's rights were violated in some other way. The courts have held that Ray's plea was freely given.

``There might have been other people involved. But to say because others were involved Ray should be released from jail is just nuts,'' Campbell said.

Ray contends he bought the rifle in Alabama and brought it to Memphis on instructions from a shadowy gun runner he knew only as Raoul. He says Raoul apparently arranged for it to be dropped near the murder scene.

Authorities have never established that Raoul existed.

Pepper contends Ray pleaded guilty because he had no other choice, since the evidence had been stacked against him.