FAIRMONT, W.Va. (AP) _ When authorities in West Virginia and Texas wanted convictions in tough investigations, they called on chemist Fred Zain to examine blood, semen and hair samples.

However, officials say his results during 13 years with West Virginia's state police crime lab were too good, and sometimes led to convictions of innocent people.

Zain's trial, on three counts of felony perjury related to testimony in a double-murder case, was scheduled to begin today.

From West Virginia, Zain went to Texas in 1989 as chief serologist for the county medical examiner's office in San Antonio.

Now, three West Virginia convictions to which he contributed have been overturned, as have two in Texas. About 70 cases have been sent back to court to determine if acquittals or new trials are necessary.

``It's reduced confidence in jury verdicts in part because the underlying assumption in the court system is that people under oath tell the truth, particularly if they're in uniform,'' said George Castelle, a public defender in Kanawha County, which includes Charleston.

Zain, 43, of Daytona Beach, Fla., was indicted last July on charges he lied in court about unperformed tests, academic credentials and how much he was paid.

Even after going to Texas, Zain had continued to be called to examine evidence in West Virginia cases.

``Police investigators and prosecutors around the state forwarded evidence to Fred Zain in Texas so that they could continue to get perfect results,'' Castelle said.

Then the state Supreme Court concluded in December 1993 that Zain's work could not be trusted, after a panel examined 36 of his cases and found evidence of fabrication in all.

His work had come into question after the state paid $1 million in 1992 to settle a threatened lawsuit by a man who had served five years of a life sentence for two rapes he didn't commit.

Zain's trial involves his testimony in the 1991 case of Paul Walker, charged in two killings.

Walker's status is not in question. He pleaded guilty to two counts of first-degree murder four days into his trial. His brother, Teddy, was convicted of the same murders in a separate trial in 1990.

Former prosecutor Roger Perry said conflicting testimony between Zain and a trooper forced the prosecution into a deal that makes Paul Walker eligible for parole after 20 years.

``You had him saying one thing and the state police saying something different and it was a question of who was the jury going to believe,'' said Perry, now a judge.

Zain testified that hairs found on one victim's robe were similar to Teddy Walker's and not Paul Walker's or the two victims' garments.

However, a state trooper told a grand jury last July that the samples never left his lab and Zain, then in Texas, had no opportunity to examine them.

Zain has refused to comment.

He was fired in July 1993 in Texas, where he faces charges in three cases.