Judge Carlos A. Samour Jr. said Jana Winter would not have to testify Wednesday in a pretrial hearing, The Denver Post said.
Winter, a New York investigative journalist, was sent to Aurora, Colo., last year to cover the July theater shooting that killed 12 people and wounded 58 during a midnight screening of "The Dark Knight Rises."
While there, Winter filed a story citing two anonymous law enforcement sources saying alleged shooter James Holmes had sent a journal filled with violent threats and drawings to his psychiatrist just before carrying out the act.
Holmes' defense team was livid at the prosecution leak, saying it violated gag orders issued by a judge in the days after the shooting. Holmes' lawyers were granted authority to begin a search to identify Winter's source.
After initial questioning of a dozen law enforcement personnel yielded nothing, Holmes' lawyers subpoenaed Winter, who said if she is called to testify she will not reveal her source and could face six months in jail for contempt of court.
The journalism community has rallied around Winter's plight.
Samour ruled the diary is potentially protected by Holmes' doctor-patient privilege and wouldn't be considered for evidence unless Holmes' defense team mounts an insanity defense.
Barring such an outcome, Samour said the diary's contents -- and the identities of those who leaked it to Winter -- aren't important enough to the case to compel Winter to testify.