Holmes, a former neuroscience graduate student, is accused of opening fire on July 20 at a midnight screening of the Batman movie "The Dark Knight Rises" in Aurora, a Denver suburb. Twelve people were killed and 58 were wounded in the attack.
A court official declined to confirm the report of the additional charges.
Holmes, 24, already faces 24 counts of first-degree murder and 116 counts of attempted murder. Under Colorado law, the doubling of charges allows prosecutors to have two pathways to secure a conviction.
The newspaper noted that a separate motion was filed to amend 16 counts of attempted murder and one count of crime-of-violence sentence enhancement against Holmes, although it did not reveal how they would be amended.
Prosecutor Rich Orman said at a hearing last month that Holmes bought a ticket to the midnight screening, then left the theater through an exit door that propped open on his way out.
Holmes then put on a gas mask and ballistic protective gear before returning to the theater and spraying the crowd with gunfire, Orman said.
Wednesday's developments came a day before the scheduled continuation of a hearing on whether a parcel Holmes sent to University of Colorado psychiatrist Lynne Fenton falls under patient-doctor privilege.
Fenton testified at an earlier hearing that she treated Holmes more than a month before the rampage, but that their professional relationship had ended well before he mailed the package to her a day before the massacre.
