BOISE, Idaho -

Condemned killer Zane Jack Fields' latest bid for a new trial has been rejected after the Idaho Supreme Court concluded his claims weren't supported by admissible evidence.

Justices Wednesday upheld a state court's dismissal of Field's sixth appeal for relief following his conviction two decades ago.

Prosecutors say Fields, of Idaho Falls, stabbed 69-year-old Mary Katherine Vanderford to death Feb. 11, 1988 while stealing about $50 from her Boise store.

He was convicted in 1991 and sentenced to die.

In his appeal, Fields said he is innocent and contends other prisoners lied to authorities that he claimed responsibility for Vanderford's death.

But justices concluded a 4th District Court judge properly dismissed Fields' claim not only because it wasn't supported by admissible evidence, but also because he'd missed deadlines.