Karr, 41, flew from Los Angeles in a turbo-prop airplane operated by the Colorado State Patrol. Shortly after the plane landed at Jefferson County Airport, Karr was transferred to a sport utility vehicle for the short trip to Boulder, where District Attorney Mary Lacy was expected to file charges almost immediately, the Denver Post reported.
Prosecutors said they have used evidence not previously disclosed to build their case against Karr.
The Boulder County District Attorney's Office said in a court document filed Wednesday that the office is still in the "very early stages" of building a case against the suspect, the Post reported.
The office is expected to test Karr for a match to DNA found in the 6-year-old girl's underwear, as well as a palm print on the door to the wine cellar where the child's body was found, a partial boot print discovered at the scene and hair and fibers taken from the body, USA Today reported.
The district attorney is expected to push for a handwriting sample from Karr to be compared to a ransom note left at the scene of the killing.
The district attorney's office asked the court Wednesday not to unseal the arrest-warrant affidavit, which could contain descriptions of the evidence used to issue the probable-cause warrant against Karr, the Post said. The document is an open record in most cases.
Pregnant Mila Kunis wins 'Best Villain' at MTV Movie Awards
Charlize Theron not engaged to Sean Penn 'yet'