Mick Philpott wrote to a friend about how he and his wife would "rape each other" after being cleared of starting the blaze that killed six of his children.
On Thursday, Philpott, known as Shameless Mick, and his wife Mairead will be jailed after being convicted of manslaughter.
In the aftermath of the fire that tore through their Derby council home on May 11 last year, the 56-year-old father of 17 wrote to a friend that he and his 32-year-old wife would be freed and "get pissed".
Then after spending a day at his victims' graves, he and his wife would "rape each other", he wrote to friend Mick Russell last July while remanded in custody.
Philpott, who had previously been jailed for seven years for repeatedly stabbing a girlfriend and attacking her mother, says in the four-page letter: "God, when we are free, which we will be, we're all going to get pissed."
In the letter, reported widely on Thursday, he insists the couple are innocent and adds: "But me and my darling beloved wife, the most important thing that we will do when this happens is to spend the whole day with our babies, at the graveside.
"We don't care if it's raining, gale force winds, snowing, I'm going straight up there.
"Then we shall probably, no, we will, rape each other... then we can all celebrate our freedom as long as they get the bastards."
He goes on: "All we care about is justice for our beautiful angels. They are keeping us so strong together .
"We will walk free and this will cost them coppers some money.
"I can't believe we are in these hell holes but you know me I'm f****** strong and I promise you both me and my beautiful wife are going to stay strong. We will walk free.
"What the hell are they doing? We all know who's done this.
"Them dirty bastards took away our pride and joys, they took away our most precious sweet beautiful baby angels.
"They've taken everything me and Mairead dreamed of and made real."