WICHITA, Kansas -- One year ago Thursday, Dennis Rader became the prime BTK suspect. Now a code written by the convicted killer is cracked.

Rader told police the code said "Let Beattie Know," but even Rader couldn’t figure out how he got that. Now the man mentioned in the solution says he has the answer.

A series of letters and numbers appeared on the top of that first letter to the Wichita Eagle in March of 2004. After Rader was arrested, he told investigators the code translated into the words "Let Beattie Know" but he couldn’t figure out how he got there.

"He did for hours try to figure it out when the police were still going, ’don’t worry about it,’" said Beattie. "At breaks, he was, ’I gotta figure this out, I gotta figure this out.’"

So BTK author Robert Beattie, who Rader says he was referring to in the code, decided to give it a try.

"The underlying reason is, I wanted to see if it really was the solution ’Let Beattie Know’ and if there was any other message there such as a victim," said Beattie.

He studied up on German fractional code then went to work. Rader told investigators the key was "PIANO" -- his code name for Vickey Wagerly. So the word PIANO was the first line in a grid. Then Beattie filled in rest of the letters of the alphabet in alphabetical order, omitting the letters of piano. Then each letter from the Wagerly correspondence was matched across to a number combination. The "T" for example equated to 4,4. The letter "N" equated to 4,1. Those letters were then written across in two rows. Then those numbers, which formed a fraction, matched again to the letters to spell out the solution.

But just to make sure Beattie had it right, we asked Wichita State University mathematics professor and native German, Christopher Wolf, to take a look.

"I can’t say it with 100% certainty that every code can correspond with everything unless you know the key and the only person who knows the key is the person who made the code. But it sounds very reasonable to assume that it’s correct," said Wolf.

And for Beattie, he now has more confirmation that his book is what brought BTK out of hiding.

"It’s interesting to know that his first message, even though it was in code, was "Let Beattie Know,’" said Beattie.

The first set of letters of code that began with a "G" was supposed to be the key but Beattie says, in true Dennis Rader form, it was misspelled.