Marshall Frank, a retired Miami-Dade homicide captain who supervised 3,000 murder investigations, declared last month that he believed Death Row inmate James Duckett, a small-town cop condemned for the on-duty 1987 rape-murder of an 11-year-old schoolgirl, was an innocent man.

Now, after more than a thousand hours and nine months of reinvestigation of the death of Teresa McAbee, the veteran homicide cop says he has identified the true killer:

James Duckett.

''I got it wrong. He did it,'' Frank said. ``I feel like such a damn fool. It's emotional. The revelation is shattering for me.''

What changed his mind was evidence that Duckett was lying to him, a collapsed alibi and a Death Row interrogation.

But there is more, much more. ''I suspect he is a serial killer, somebody who has a compulsive urge to kill and to do it again,'' Frank said.

The opinion of Maj. W.J. Martin, chief of criminal investigations of the Polk County sheriff's department, is that James Duckett is the killer who strangled Jennifer Weldon, 14, a few months after the McAbee crime. ''He is absolutely our prime suspect,'' Martin said. He may well be linked to other homicides.

''I've been depressed for the last couple of days,'' Frank said. ``I can't get this out of my head. I've put in a thousand hours of my own time, put 3,000 miles on my car and spent untold dollars -- all because I had a sense of humanity. I don't think anybody innocent should ever suffer prison, especially Death Row. That's all it was.''

Frank realized he was wrong, he says, when sheriff's detectives in Lake County opened the McAbee case file to him, and Polk County sheriff's detectives revealed their cases.

Then came a three-hour face-to-face Death Row interview, in which, he says, Duckett lied to him on crucial points.

Under the watchful supervision of a corrections officer, Frank and Duckett shared Cokes and microwaved chicken sandwiches from a vending machine in a visitors room reserved exclusively for Death Row inmates at Florida State Prison. The Father's Day meeting was their first after exchanging 30 letters.

''It was like we were having a couple of drinks at a bar,'' Frank said. Duckett, a hefty 275 pounds, ``was laughing, a big-bellied, wide-open-mouthed laugh, looking at me with eyes that didn't blink, smiling all the time. He didn't flinch. No sense of guilt.''

At the time of Teresa's murder on May 11, 1987, Duckett, then 29, was on patrol during a 7 p.m. to 7 a.m. shift. Shortly after 10 p.m., he spotted Teresa McAbee with a 16-year-old Mexican boy behind a trash bin outside the Circle K convenience store.

Duckett, a rookie police officer in a five-man department in the Central Florida town of Mascotte, questioned the youngsters and warned them about a 10:30 p.m. curfew. He said Teresa walked off toward her home, just 400 feet away.

The girl's mother reported her missing at midnight. A fisherman found the child fully dressed the next morning, face down in Knight Lake, near a pump house about 2,000 feet from the convenience store. She had been strangled. Duckett was convicted a year later.

Frank didn't hear of the case until last year. Retired from the Miami-Dade police department after 30 years, he'd begun to write novels in North Carolina after a stint as a Wackenhut executive and came across the case while researching a book.

DIFFERENT PERSPECTIVE

Ex-officer was convinced

that inmate was innocent

Three damning factors helped convict Duckett. Fifteen years later, the same evidence convinced Frank that Duckett was innocent.

Gwen Gurley, 16, pregnant and in trouble with the law, testified in a videotaped deposition that she saw Duckett drive away from the Circle K convenience store with Teresa in his patrol car the night of the murder. A friend backed her up.

Both later recanted. Gurley said she lied in exchange for favors from police and to be able to give birth outside jail. The friend admitted that she, too, lied.

But during a 1997 Duckett appeal proceeding, Gurley refused to repeat the story under oath, fearing prosecution on perjury charges. She took the Fifth Amendment.

''No person should ever go to Death Row based on the testimony of a jailhouse snitch, and that's what Gwen Gurley was,'' Frank said.

Other evidence against Duckett seemed suspect. Michael Malone, a former FBI crime lab expert, testified to the high probability that a pubic hair found in the dead girl's panties belonged to Duckett. He did so after two other certified labs could not. His FBI lab work has since come under fire in scores of other cases.

And tire tracks near the murder scene were not ''matched'' to Duckett's patrol car, but were the same pattern -- mud and snow tires more common in Northern states than in the South. Logically, they could have come from other police cars at the scene.

The testimony of three young women who said that Duckett made sexual overtures to them while on duty in his patrol car also seemed weak to Frank. Two swore that Duckett told them he liked ``little girls.''

But one such encounter reportedly occurred on a Friday, Duckett's day off. On the witness stand, Duckett vehemently denied it.

In poring through thousands of pages of reports, Frank found, however, that the incident in question had not occurred on a Friday after all, and that many people had confirmed the young women's stories.

''At least five people gave statements saying that Linda Upshaw was upset about Duckett's actions before she ever talked to the sheriff's detectives,'' Frank said.

The Polk County connection occurred while Duckett was a suspect in Teresa's murder. Fired from the police department, Duckett was working as a night-shift laborer at a phosphate mine in Polk County for $7.50 an hour. That's when someone murdered 14-year-old Jennifer Weldon.

Jennifer was last seen on Sept. 19, 1987, walking home alone on Highway 98 just north of Lakeland, returning from a carnival. She carried a lime green shopping bag containing a stuffed animal, Frank says.

Duckett drove the same route to work, Maj. Martin said. Her decomposed body was found Oct. 2, in a remote region of the county near a phosphate mine. Gasoline receipts placed Duckett close by. The night of the murder, he arrived at work disheveled and two hours late, police said.

AN EARLIER MURDER

A young woman, strangled,

was found in water-filled pit

When the girl's body was found, her green shopping bag and stuffed toy were missing. Polk County investigators said that after Duckett's arrest in Teresa's murder, they went to see his wife, Carla. She told them about a stuffed animal that her husband brought home at the time of Jennifer's disappearance. It was in a lime green shopping bag. She said she had been angry because he brought only one and they had two children, Frank said. Polk County police said a relative ``got rid of the toy.''

Almost exactly a year before Teresa's death, an eerily similar murder occurred in Polk on May 7, 1986. A petite, still unidentified young woman was found, fully clothed, floating face down in a water-filled pit off Highway 33 near Lakeland. She, too, had been strangled.

She was five feet two inches tall, with reddish brown hair and eyes blue to hazel. Her clothing, jewelry and tattoos were distinctive. She wore an aqua blue shirt and jeans, and her belt of red and blue ribbons had beads and feathers on the ends. Bells were tied to the laces of her tennis shoes.

She loved hearts. White stones shaped like hearts adorned one of three silver-colored bracelets. Five hearts, three with blue stones and two with red, decorated one of her two silver rings.

In triple-pierced ears, she wore three pairs of earrings -- one heart-shaped, in light blue, another in a gold heart design, and the third a pair of gold French hoops. A hand-drawn heart was tattooed on her left hip and a question mark on her right hip. The inside of her left wrist bore a yellow rose, and a long-stemmed red rose shared her right groin with a black unicorn.

Maj. Martin still hopes the ''Queen of Hearts'' will be identified and her murder solved. A girl who looked like the victim, Martin said, was last seen getting into a dark blue car. Duckett drove a royal blue Buick Regal at the time.

Years ago, a teenage girl told Polk detectives of a frightening encounter with Duckett. He'd offered to drive her home, but took her instead to a remote trailer, where he became sexually aggressive.

The girl, thinking quickly, told him a whole bunch of people ''know I'm with you.'' With that, he took her home. The trailer was three miles from where Jennifer Weldon's corpse was found years later.

On a scale of one to 10, what are the chances that Duckett killed Jennifer Weldon? ''Eleven,'' Martin replied.

Only last month, Frank insisted that the chances of Duckett having committed the McAbee murder were ``zero.''

''It may be embarrassing to me, but it's a good thing that all this has come out,'' he said. ``I think we're identifying somebody who's very dangerous.''

TESTING FOR THE TRUTH

`I wanted to see how many

lies I could elicit from him'

By the time of his Death Row interview, Frank no longer believed Duckett. But he did not confront him directly about his truthfulness. ``I wanted to see how many lies I could elicit from him.''

When talking about the three young women, ''Duckett kept denying it, saying they all lied,'' Frank said. ``It's wrong to solicit sex on duty, but unfortunately it happens. In spite of my assuring him that such behavior is not that uncommon for young uniformed cops, he remained dishonest. That was pretty stupid of him.''

But more important were Duckett's notebook entries cited in his appeals as proof of his innocence.

One note mentions a 10:58 p.m. ''well-being'' check he made at a Jiffy Stop convenience store the night of the murder. Someone requested that police check on the clerk when the phone remained busy. The call would have been a solid alibi because it occurred at the probable time Teresa McAbee was murdered.

Frank now believes the entry was faked. The notebook was never offered by the defense at Duckett's trial, and Frank said, ``If true, it was a perfect alibi. He had written it in his notebook, but didn't say anything when he was interrogated because the cops would've checked it out with the clerk and learned it wasn't true.''

And only one page of the notebook that Frank examined had a date. It was the day of the murder. Frank now thinks Duckett wrote it in after the crime.

''I made Duckett go over and over it, first in letters, and then in person,'' Frank said. ``Finally, it dawned on me. There was no well-being call, no Jiffy Stop check. If someone accused me of committing a murder at 11 p.m. and I was innocent, I would remember every second, what I was doing, where I was and who could verify.''

Yet, he said, when he asked Duckett why he didn't do so, he replied, ``I don't know why I never said anything.''

''Another inconsistency was his inability to remember how he got that call, because it was not via police radio,'' Frank said. 'His radio that night was silent for two hours. Duckett `thinks' it was a phone call about the Jiffy Stop's busy line.''

If that were accurate, Duckett would have had two alibi witnesses -- the caller and the clerk. ''Duckett trapped himself in a telltale lie,'' Frank said.

FALSIFIED ENTRIES?

Ex-policeman raises doubts

about convicted man's story

Falsified entries could explain why Duckett claimed that Teresa was wearing a blue-green blouse when he questioned her at the Circle K. He might well have made it up after the crime, Frank now believes. When found dead in the lake, she was wearing a white and tan striped shirt. Frank now thinks that Duckett was trying to make police believe that she got home safely and changed her clothes. The mother said she never came home.

When asked about the Weldon case during the Death Row interview, Duckett looked down for about 45 seconds without eye contact, Frank said.

Frank also now doubts a witness in the McAbee case who said that from the laundromat next door, he saw the little girl get into a small blue car. He may have seen her earlier that night when her mother picked her up.

Some questions Frank may never answer, such as the eerie behavior of the little girl's aunt. Supposedly, she called relatives before Teresa's body was found to say the girl was in the lake.

Another puzzle: Circle K clerk Shirley Williams, who said Duckett returned to the store at 11:10 p.m. She, too, may have been mistaken about the time, Frank suspects.

No one seemed certain about times. The site where Teresa was found was only one minute away. Two other witnesses went to the store to rent a movie at 10:40 that night. They said they saw Duckett talking to Teresa. Their receipt was time-dated at 10:45 p.m.

''I feel upside down,'' Frank said. ``It's a good lesson. Even old salts have a lot to learn sometimes.''

When he went public with his belief in Duckett's innocence, the national television networks sprang into action. 60 Minutes, 48 hours and ABC's Prime Time all contacted Frank, each eager for an exclusive story. Frank chose ABC. A film crew was preparing to come to Florida. Duckett's attorney had already shipped 25 pounds of defense documents to the network.

Frank said he really thought he could back up his belief in Duckett's innocence. ''Right now,'' he said, ``I feel like traveling to England and staying there for the next 10 years and to hell with all this. But this work has uncovered more good than bad. Now we've gotten the truth out. I have no problem with executing a Ted Bundy or a Jeffrey Dahmer.''

Asked if Duckett is less dangerous, he said, ``No, just less successful.''

The two men shook hands at the end of their Death Row visit. 'I looked him in the eye and said, `Good luck,' '' Frank said. ``I think he thought I was his guardian angel.''

Defense attorney Beth Wells had refused for five months to allow Frank to see her client. ''She knew I was a cop,'' he said. ``She didn't trust me -- for good reason.''