Bigshot Publicist to Hollywood Murder Tipster: I Owe You Nothing!

The man who claims he helped police track down the murderer of famed Hollywood publicist Ronni Chasen is barking up the wrong tree -- according to the publicist he's suing.

As we previously reported, the tipster -- who identifies himself as John Doe -- sued bigshot publicist Michael Levine (left), claiming Levine offered a $25,000 reward for information leading to the capture of Chasen's gunman ... but never paid up.

Mr. Doe also sued Palm Springs Film Festival honcho Harold Matzner -- claiming Matzner offered a $100k reward for the same information.

But Levine's lawyer shot back yesterday with a blistering letter to John Doe's attorney -- insisting Levine never promised to ante up $25,000.

Levine's lawyer, Eric George, claims in the letter -- obtained by TMZ -- Levine never actually offered a reward and abandoned the effort early on at the request of Chasen's family.