In his time as a New York City police officer, Stephen Spiro says that it only happened to him once.

Typically, the people he arrested wanted nothing to do with him.

But then, few things about the case of Mark David Chapman were typical.

Chapman, the man convicted of killing former Beatle John Lennon, wrote Spiro, his arresting officer, four letters.

In the letters, Chapman repeatedly tells Spiro to read "The Catcher in the Rye," saying the book would explain much of what happened the night of the murder, December 8, 1980.

He expresses an ease with the officer, saying he hoped they could be friends, that he thought Spiro was a great policeman, and that he had felt close to him ever since his arrest.

Chillingly, Chapman also wrote that others "could -- and would -- have served the same purpose" as Lennon.

The four letters are expected to go on sale Monday on the Moments in Time website, which sells rare autographs and historical documents.

Spiro says they represent the only time someone he arrested wrote him letters.

"They've been in my possession for 30 years, and I'm 66 years old, and I'm saying, you know, what am I going to do with these things? So I figured I'd sell them," he told CNN.

The letters run from January to May 1983. Each one is typed and includes Chapman's signature.

Spiro says he wrote a few letters in return, but Chapman "cut it off after a while."

The two men spent several hours together immediately after Chapman's arrest. He trusted Spiro.

Chapman, who was denied parole for the seventh time in August, is serving a sentence of 20 years to life.

The letters will be on sale for $75,000, said Gary Zimet, who runs the Moments in Time site.

The site is also selling a "Double Fantasy" record album, which Lennon signed for Chapman before his murder, for $650,000.

Spiro said that he plans to donate some of the money he makes to a local shelter for battered women.

Here are excerpts from Chapman's letters:

January 15, 1983

" ... I am glad that we can keep in touch. I'll not forget the first time we met ...