In a letter written from a Colorado prison to pen pal Jannie Coverdale, Nichols also said he grieves "daily knowing that I had a part in such a devastating tragedy," The (Oklahoma City) Oklahoman reported Monday.
For years Nichols denied involvement in the deadly 1995 Oklahoma City federal building bombing. However, in 2005, he admitted to family and the FBI his role in making the bomb, and then later told the FBI he thought Timothy McVeigh planned a nighttime attack on a monument or similar structure.
McVeigh detonated a truck bomb outside the Alfred P. Murrah Federal Building April 19, 1995, resulting in 168 deaths and hundreds of injuries. McVeigh was executed in 2001.
Nichols writes regularly to Coverdale, an Oklahoma City woman whose two grandsons were among the 19 children who died in the explosion, the newspaper said. She shared her two-year correspondence with The Oklahoman.
The newspaper said Coverdale is among those who believe others besides Nichols and McVeigh were involved in the bombing. She said she started writing to Nichols, hoping he would reveal any other participants; however, she now says she thinks Nichols knows very little.
Nichols is serving life terms in the federal prison in Florence, Colo., and cannot be paroled or released.
In an April 2010 letter, Nichols said the bombing was "just so wrong. There was really no justification for it."
In an August 2010 letter, Nichols said McVeigh didn't tell him the federal building was the target, "but he did say he was going to make 'his statement' at night. And from what he said [indirectly] that it was not going to be an occupied structure, leading me to believe it was going to be some type of monument, bridge or similar structure and thus no loss of lives."