He says the casinos have been cheating for the past 20 years.
Nowhere in the letter, dated May 25th, does Magee reference Ray Kot, who he allegedly shot and killed.
There are no threats in the letter. Magee does apologize for the way the letter is written, saying he is writing it under a "degree of stress." 6abc has decided not to publish the entire contents of the letter.
The station contacted police, and is cooperating with the investigation.
Magee was in court Thursday afternoon, charged with first degree murder for gunning down a shift manager Raymond Kot on Wednesday afternoon.
The shooting happened in a private room off the casino floor.
No patrons were injured.
In court documents, investigators say Magee used illegal hollow-nose bullets, designed to inflict maximum damage.
Magee apparently knew the victim, Raymond Kot, from previous trips to the Atlantic City casino. Kot, 55, had worked for the Taj Mahal since the day it opened in 1990.
Mark Juliano, CEO of Trump Entertainment Resorts, which runs the casino, said Thursday the shooter had no previous beef with supervisor Raymond Kot, who had been with the Taj Mahal since it opened in 1990.
Juliano told The Associated Press that Mark Magee was carrying a suicide note and had intended to shoot himself or jump from the parking garage Wednesday afternoon but surrendered meekly when police apprehended him.
"It's too bad he didn't do it first," Juliano said. "He was obviously an extremely disturbed, sick individual."
The contents of the note weren't revealed by authorities.
Kot leaves behind a wife and a high-school aged son. He got the news of his father's death while on a school trip to Costa Rica.
At his initial court appearance Thursday afternoon in Mays Landing, Magee spoke only to acknowledge that he understood the charges against him. The proceeding took less than three minutes. Prosecutors revealed nothing about a possible motive.
Among the weapons offenses, Magee is charged with possession of hollow-nose bullets, which are illegal in New Jersey.
Donald Trump, who is no longer associated with the gambling company he used to run, says fellow workers respected and looked up to Kot.
"He was a wonderful, loyal person who worked for me for a long time," the real estate tycoon and "Celebrity Apprentice" TV star told The Associated Press on Thursday. "He was somebody the other employees liked very much. He was a very solid citizen."
Kot was shot several times in the abdomen in an office just off the casino floor, an area not visible to casino patrons. He died about 2 1/2 hours later at Atlantic City Medical Center after undergoing surgery.
Magee surrendered to police in a parking garage.
The Associated Press contributed to this report