(Reuters) - California Gov. Jerry Brown ordered late Monday that a man sitting on death row for a quadruple murder must have one more attempt to prove he is innocent of hacking a family to death with a hatchet more than 30 years ago.

In an executive order issued Christmas Eve, Brown declared that four pieces of key evidence be retested for DNA that might exonerate death row inmate Kevin Cooper, 60, who has maintained his innocence since his 1985 conviction for the murder of a San Bernardino, California family and one of their neighbors.

Cooper, who is in San Quentin State Prison, was convicted for the 1983 hatchet homicides of Douglas and Peggy Ryen, both 41, their daughter Jessica, 10, and neighbor Christopher Hughes, 11, according to the order.

Another child of the Ryens, eight-year-old Josh, was severely injured but survived.

At the time of the murder, Cooper was an escaped inmate who was hiding out in an empty house in the Ryens’ neighborhood, the Los Angeles Times reported. A bloody hatchet sheath was found days after the crime in Cooper’s hideout house, and a hatchet in the grass nearby, the paper reported.

But Cooper has claimed for more than 30 years that he did not carry out the attack.

“Mr. Cooper maintains that evidence against him was planted, tainted or destroyed by law enforcement,” Brown wrote in his order, posted on the Governor’s official website.

Brown ordered that four pieces of evidence be retested - a tan shirt, an orange towel, a hatchet handle and a hatchet sheath.

The order notes that the acting San Bernardino County District Attorney contends that Cooper’s claims of innocence were already tested by the courts over the years and that previous DNA tests link Cooper to the crime.

Gov. Brown wrote in his order, “I take no position as to Mr. Cooper’s guilt or innocence at this time, but colorable factual questions have been raised about whether advances in DNA technology warrant limited retesting of certain physical evidence at this time.”

Cooper has unsuccessfully asked for clemency twice before.

The Los Angeles Times reported in July that at least three jurors in the case have since expressed their doubts about Cooper’s guilt and said that the state might have the wrong man in prison.