Mitchell Rupe, a former death row inmate once found too heavy to hang, died at the Washington State Penitentiary in Walla Walla following a long illness. He was 51.
Spokeswoman Lori Scamahorn said Rupe died yesterday at the hospital inside the prison grounds.
He had been there since January 3.
Rupe shot two Olympia bank cashiers to death at point-blank range during a 1981 robbery.
Juries twice sentenced him to death, but higher courts overturned the sentences.
In 1994, a federal judge upheld his conviction but agreed with Rupe’s contention that at 400 pounds (more than 25 stone), he was too heavy to hang because of the risk of decapitation.
Rupe argued that would be cruel and unusual punishment.
At the time, Washington’s only manner of execution was hanging.
The main method now is lethal injection.
Prosecutors tried for the death penalty a third time in 2000, but a jury deadlocked 11-1 – just shy of the unanimous vote required for capital punishment.