No one made much of an effort Friday to vouch for the credibility of Frank Zuccarello, a jailhouse informant whose testimony helped put four people in prison for murders in Miami-Dade and Broward.

Prosecutors said there was no need.

Zuccarello is an admitted home invader whose accounts helped deliver convictions in two notorious murder cases from 1986: the slaying of millionaire Miami developer Stanley Cohen and the killing of 11-year-old Staci Jazvac in Broward.

After years of legal impasse, a defense attorney hopes to prove once and for all that Zuccarello was lying. The stakes are high. There was little but Zuccarello's story to support the conviction of Anthony Caracciolo as the man who shot and killed Cohen.

''A manifest injustice has been done, because an innocent man is behind bars,'' said Rhonda Anderson, attorney for Caracciolo, speaking in a hearing before Miami-Dade Circuit Judge Lawrence Schwartz. Schwartz said he will issue a ruling next month.

Miami-Dade prosecutors assailed Caracciolo's ''newly discovered evidence'' as more rehash: leftovers from the 1989 Cohen murder trial, reheated and dressed up as new.

''The claim, essentially, is that Frank Zuccarello is a liar,'' said Assistant State Attorney Abe Laeser. ``That claim has been hanging around the state's neck since the summer of 1986, when Stanley Cohen died.''

Arrested for a string of home-invasion robberies in 1986, Zuccarello turned informant and started talking about high-profile murder cases.

He told police that widow Joyce Cohen had hired him, Caracciolo and a third man, Tommy Joslin, to murder her husband in his bed. He also said a cellmate named Michael Rivera had admitted to the murder of Staci Jazvac, a girl of 11 who was pulled from her bicycle, murdered and dumped in a field in Coral Springs.

Rivera was sent to Death Row in 1987 for the Jazvac slaying. A jury convicted Joyce Cohen of her husband's murder in 1989. Caracciolo and Joslin pleaded no contest to the Cohen murder in 1990.

Zuccarello, charged with 23 felonies, got out of prison after 2 ½ years on a plea agreement.

Caracciolo's bid for a full evidentiary hearing is based on new evidence of perjury by Zuccarello:

• A 1999 affidavit from Broward Sheriff's criminal investigations chief Tony Fantigrassi. The BSO major says Zuccarello made statements ''suggesting he had lied in the Cohen case'' and that he considers Zuccarello ``an untrustworthy witness.''

• 1999 affidavits from two other law enforcers casting doubt on Zuccarello's credibility.

• 1998 sworn statements from a TV news reporter and cameraman stating that a Miami police investigator told them Caracciolo had no role in the slaying.

• Evidence that several law enforcers shared misgivings about Zuccarello with Dade prosecutors as early as 1989 and that the prosecutors kept the information to themselves.

But prosecutors questioned Friday whether any of the evidence is really new.

The rules that govern Florida courts place a two-year time limit on motions to vacate a sentence in most cases. One exception: newly discovered evidence that was previously unknown to the defendant and could not have been found through ``due diligence''.

A stack of new statements questioning Zuccarello's credibility, prosecutors said, do not add up to new evidence.

''These are new affidavits. But not new issues,'' Laeser said Friday. ``There has to be a sense of finality in these cases.''

Anderson countered that the damaging statements weren't publicly known until the late 1990s. Caracciolo had no lawyer and wrote court filings by hand through much of that period.

The convict did not attend the hearing. But his uncle, Joe Caracciolo, was there.

''I believe he's innocent,'' the elder Caracciolo said. ``I know he's innocent.''