Sources at the Post describe Mr. Weiss’ imminent departure as a major loss for the paper.

Mr. Weiss has worked at The Post for roughly 25 years, along the way cranking out countless Page 1 exclusives on subjects ranging from the organized crime to homeland security to high profile crimes.

According to sources, Mr. Weiss is not leaving for another job. He did not return several phone calls seeking comment.

Mr. Weiss is the author of two books, including The Man Who Warned America: The Life and Death of John O’Neil the FBI’s Embattled Counterterror Warrior, which HarperCollins published in 2004.  

Amid the recent thawing of New York’s media market, a number of notable staffers have recently departed from the Post, including Neal Shah, Maggie Haberman, and Peter Lauria--to name a few.

Mr. Weiss is by far the biggest star to leave the paper.

“He has an encyclopedic grasp of the police department and law enforcement in general,” said his colleague, reporter Philip Messing. “In addition to good sources, he’s an indefatigable worker.”

“He’ll be missed greatly,” he added.

UPDATE: Here's a copy of the resignation letter Mr. Weiss sent to Post editor Col Allan:

Dear Col,
    As you know from recent conversations, I have been dealing with various serious family health issues for some time now. As a result, I regret to inform you that I intend to resign from my employment at the New York Post next Friday June 18.
    It has been a privilege working for The Post and I am proud to have contributed to the great news tradition of The Post.
    On a personal note, I want to thank you for the courtesy you have extended over the many years we have worked together at a newspaper I have called my second home for 24 years.
   I wish you, all of my colleagues and The Post, continued success in the years ahead.
   Sincerely,
   Murray Weiss