Family killer Chris Watts spends his days in solitary confinement with just one hour a day outside his cell for showering and exercise, according to reports.
The monster is "sad" and wishes he would have "handled things differently" after being jailed for life for murdering his pregnant wife and daughters, it is claimed.
Watts is in a 23-hour lockdown in a prison in the US state of Wisconsin, with timeout staggered so he doesn't have any contact with other prisoners.
He remains in an evaluation unit of the prison.
The friend claims Watts - who strangled his wife Shanann and smothered his daughters Bella, four, and Celeste, three - has spent a lot of time reflecting on the murders and wishes he could turn back the clock.
The friend, named only as Kim, told People: “He’s sad that everyone is hurting.
"He wishes he could go back in time. He wishes he had handled things differently.”
She described how Watts spends his days in a prison almost 1,000 miles away from Frederick, Colorado, where he carried out the murders in August 2018.
When he is in his cell for 23 hours a day he has little to do and is allowed to have a Bible, but not much more, Kim claims.
Watts, 33, has received dozens of letters and photos from female admirers from around the world, but it is unclear if any of them have been delivered to his cell.
He had previously told Colorado authorities while in prison there that he speaks to photos of his family in his cell and reads a book out loud every night to the daughters he murdered.
He was having an affair with a colleague and had claimed to his mistress that he and his wife were no longer together, and he was looking for a place of his own.
The marriage had been going through a difficult period, and there was an indication that Watts didn't want a third child.
Few details about the motive and the crime emerged in court when Watts was jailed for life for murder and other offences.
A lawyer involved in the case has since claimed that the dad confessed to strangling Shanann, 34, after an argument about a divorce, and then put her body and the girls, who were alive at the time, in his truck.
Watts drove to the oil site where he worked and smothered both girls with a blanket in the back of the vehicle.
He buried Shanann in a shallow grave and stuffed the girls' bodies into oil tanks.
In February, he told the Colorado Bureau of Investigation in a jailhouse interview that Shanann "may have been" praying when he strangled her in their bedroom.
He said he drove her body to the work site and buried it in a shallow grave as his daughters waited in the truck.
He claimed Bella watched as he smothered Celeste and screamed "Daddy, no" before he killed her.
Watts, who is not eligible for parole, could appeal his case even though he has pleaded guilty, but to have it overturned he must prove there is new evidence or that his conviction was unconstitutional.