Judge Cormac J. Carney of the U.S. District Court for the Central District of California ruled that the state's death penalty is unconstitutional Wednesday.
The state put a hold on executions in 2005, leaving 748 people on death row, including inmate Ernest Dewayne Jones, whose execution Carney vacated.
"Allowing this system to continue to threaten Mr. Jones with the slight possibility of death, almost a generation after he was first sentenced, violates the Eighth Amendment's prohibition against cruel and unusual punishment," he wrote.
Jones was sentenced to death in 1995 for raping and killing his girlfriend's mother. Nearly half of the people on California's death row have been waiting for more than 19 years and only 13 of the 900 sentenced to death by the state since 1978 have been killed. Carney called the California death penalty system, which hasn't executed an inmate since 2006, "dysfunctional" and "arbitrary" in his 29 page ruling, writing:
When an individual is condemned to death in California, the sentence carries with it an implicit promise from the State that it will actually be carried out. That promise is made to the citizens of the State... It is made to jurors.... It is made to victims and their loved ones... And it is made to the hundreds of individuals on Death Row, as a statement their crimes are so heinous they have forfeited their right to life.
But for too long now, the promise has been an empty one."
Carney was appointed to the federal bench by President George W. Bush in 2003.
CNN legal analyst Mark Geragos said he expects prosecutors will appeal the case.