Evil Chris Watts says he wouldn't slaughtered his wife and young children if he hadn't met his mistress.
Watts was having an affair with Nichol Kessinger, the mistress he met at work and had been seeing for two months.
The 34-year-old murderer became so obsessed with Kessinger, he decided to murder his pregnant wife Shanann, and daughters Bella, four, and Celeste, three, so they could be together.
Watts even tried to poison his unborn child and cause wife Shanann to miscarry after giving her a powerful painkiller Oxycodone.
The sickening revelations come after 65-year-old grandmother Cheryln Cadle began exchanging letters with Watts - who is serving life behind bars for his heinous crimes.
Cadle has now compiled his letters in a book titled, Letters from Christopher.
In his correspondence with Cadle he admits to still being in love with Kessinger, but also laments he would not be in prison if he hadn't met her, reports the Mail .
He also admits to killing Kessinger so he could feel "free to be with Nikki".
In one letter he writes: "If I had not met Nikki, I would never have killed my family."
In another, he says: "All I could feel was now I was free to be with Nikki. Feelings of my love for her was overcoming me. I felt no remorse.
"The darkness inside of me had won, it was still in me, though, I thought maybe permanently. I felt evil, swallowed up by this thing inside of me. I felt like I could kill anything and be justified for doing it."
Watts slaughtered his family on the morning of August 13 at their home in Frederick Colorado before burying his pregnant wife in a shallow grave and dumping his daughters in oil tanks.
He has previously admitted to attempting to smother his two daughters with pillows at their home after telling Shannon he didn't love her anymore and strangling her to death.
Watts is currently serving his sentence at Dodge Correctional Institute, Watts has his own cell in a wing of around 17 inmates with special needs, close to the infirmary.
He was placed there for his own safety – along with moving Watts out of a Colorado prison in the first place.
Those who worked on the case have recently spoken of the trauma it continues to cause them.
A prosecutor said it was so traumatic for everyone involved that they are struggling to come to terms with it ten months on and they will "never be the same".
Steve Wrenn, the Deputy District Attorney for Weld County in Colorado, told Fox News: “Police officers, first responders, prosecutors, defence attorneys - we operate in a world where we see bad people do bad things on a somewhat daily basis.
"This took it to a level that I don’t think a lot of people are still able to get their heads around it. It’s impacted the way we go about our daily lives and how we interact with our families, how we are able to do our jobs sometimes.”
He added: “The first responders that had to remove the children from the oil tanks - they’ll never be the same. Some of the investigators I know had struggled to return to their jobs and go about investigations the same way.”
Mr Wrenn said it's the kind of crime that can only be committed by a sociopath.
