|Birth Date||January 10, 1977|
|Family|| Lee Mullens (father)|
Karen Bachner (mother; deceased)
George Bachner (maternal grandfather; deceased)
Claire Bachner (maternal grandmother; deceased)
Unnamed maternal aunt (status unknown)
|Pathology|| Serial Killer|
|No. of Victims|| 3 killed|
|Portrayed By|| Josh Braaten|
Michael Ketzner (young)
|First Appearance||Remembrance of Things Past|
"Dad, it's okay if you don't remember..."
See the Lee Mullens and Colby Bachner article
Along with Lee, Colby targeted Caucasian blondes in their 20s. He and Lee abducted their victims by luring them in with the ruse that one or the other was in serious need of aid before pushing her in a van and knocking her out with a blow to the head. After his victims were electrocuted and sodomized like his father's original victims, he stabbed them reluctantly alongside Lee. Colby also made the victim read from a script to reenact his father's last murders. Prior to the abductions, Colby would stalk the victims, take pictures of them, and learn their daily schedules so he could select the best options for Lee.
- Unspecified date in 1987: Karen Bachner (his mother; unknowingly subdued by him and was killed by Lee)
- Unspecified dates: At least two unnamed women (both stalked only)
- September 27-28: Kara Kirkland
- October 3-4: Jenny DeLilly
- October 5-6: Heather Langley
- October 6-7: Shelly (abducted and intended to kill; was killed by Lee)
- October 7: Anna (abducted and attempted to kill; was rescued)
- Josh Braaten, the actor who portrays Colby, previously portrayed a serial killer on the crime drama The Mentalist.