Gardner, 31, spoke with News 8 in an exclusive interview set to air at 5 p.m., and again at 6:30 and 11 p.m.
Gardner is locked up in San Diego Central Jail, pending sentencing May 14.
In exchange for pleaded guilty to raping and murdering Amber in February 2009 and Chelsea a year later, Gardner will get two consecutive life prison terms without the possibility of parole. He will also be sentenced to an additional 33 years to life for assaulting a woman on Dec. 27.
Gardner has become a lightning rod for activists who want tighter restraints on sex offenders. He had already done five years in prison for attacking a teenage girl before he killed Amber and Chelsea.
Chelsea, a 17-year-old, straight-A senior at Poway High School disappeared Feb. 25 after going for a run at Rancho Bernardo Community Park. Her body was discovered five days later in a shallow grave near a tributary of nearby Lake Hodges — not far from Gardner's mother's home where he attacked a neighbor girl in 2000.
Amber, 14, vanished while walking to Escondido High School in February 2009. Her skeletal remains were found last month in Pala.
A DNA match to semen found on Chelsea's underwear prompted Gardner's arrest. He avoided the death penalty by leading authorities to Amber's body.