At 6-foot 4-inches and more than 300 pounds, veteran FBI agent Joaquin “Jack” Garcia is a small mountain of a man who is hard to miss. That’s never stopped him from being a master of disguises. In recent years, the expert undercover agent’s appointment calendar must have read a bit like the script for the 1960s screwball comedy “If It’s Tuesday, This Must Be Belgium.”

Mr. Garcia surfaced last year when he took the stand in a closed courtroom to describe how he had played the role of a Gambino associate for 27 months. At the same time, Mr. Garcia was also posing as a New York capo in a 36-month FBI sting against crooked Florida cops in which four police officers were nailed last week on corruption charges (thus the reason for the secret testimony).

That wasn’t all: Sources tell Gang Land that Mr. Garcia worked undercover in three other successful organized crime and corruption cases during the same time frame.

In Boston, he posed as a drug lord, resulting in the indictment of three police officers last July on drug trafficking and money laundering charges. During the lengthy FBI sting operation, the cops were also implicated in steroid abuse, identity theft and other crimes. Five weeks ago, a fourth cop was charged with perjury, obstruction of justice, and trafficking in steroids.

During the same period, sources said, Mr. Garcia worked undercover in two separate cases in Atlantic City. In one involving Asian organized crime, he played the role of a wiseguy. In a political corruption probe that resulted last fall in guilty pleas by three city council members — two from Atlantic City and one from Camden — he posed as a Wall Street financier.

During the final stages of the Florida, Atlantic City, and Boston probes, Mr. Garcia, who was undercover all but two of his 26 years as an FBI agent, was retired and working as an independent contractor, according to his testimony at the trial of Gambino capo Gregory DePalma, one of 32 mobsters and associates who was convicted as a result of Mr. Garcia’s undercover work in New York.

For the record, the DePalma investigation began in December 2002 and ended in March 2005. Mr. Garcia, who retired last March, testified against DePlama last May. The Sunshine State sting operation began in February 2004 and ended last week.

“Without question, Jack Garcia is the best undercover agent the Bureau has ever had,” a veteran law enforcement official who worked with him on the DePalma case said. The family’s acting boss, Arnold “Zeke” Squitieri, and underboss, Anthony “the Genius” Megale, were among those who copped plea deals rather than go to trial with DePalma.

At trial, Mr. Garcia, a Cuban-born émigré, said he posed as a “fourth- or fifth-generation” Italian American who traced his lineage to Sicily. “The ruse was that I was a knock-around guy, a guy who had access to everything,” he testified.

Mr. Garcia’s testimony at the DePalma trial was piped into another room to prevent his cover from being blown in the Florida case. In that investigation, the cops traveled to New York and Atlantic City, according to a federal complaint filed in Miami.

Two cops allegedly delivered $400,000 in “stolen” bearer bonds to an undercover agent in New York who was posing as an underling of “Big Jack” in 2005. Last June, a month after Mr. Garcia sunk DePalma from the witness stand, the cops allegedly transported “stolen artwork” to the same “underling” in Atlantic City.

On October 26, according to the complaint, police officer Kevin Companion, the leader of the alleged rogues, met Big Jack and two “underlings” at the Borgata Hotel in Atlantic City to discuss several schemes. Out of the presence Mr. of Garcia – who acted as a non-drug dealing wiseguy in the scam — Mr. Companion agreed to provide protection for a drug shipment, and enlist his colleagues for the job.

A month later, the four cops, who were warned against mentioning “heroin or drugs” in front of Big Jack, agreed to the drug caper with Big Jack’s crew, and, after safely escorting a drug mule out of harm’s way, were videotaped receiving a total of $32,000 for their services. All told, the four took in $92,000 for their outside work, much of which was done while armed and in uniform, according to the complaint.

Sources say other cops were implicated in crimes but may escape prosecution because Mr. Companion and police officer Jeffry Courtney learned of the probe after the FBI told Chief James Scarberry about it last month and he relayed the information to his top brass and city officials.

FBI officials, not to mention Mr. Garcia and 12 other agents who worked undercover in the investigation, are furious about the leak, and are likely to point to it the next time the agency gets accused of not sharing information with local police.

On the bright side, Messrs. Companion and Courtney called in sick and began to inquire about retirement benefits when they got wind of the probe. They didn’t react the way New York’s infamous Mafia Cops, Louis Eppolito and Steven Caracappa, often did during their careers. The dark side — that the lives of FBI agents were put at risk if the Hollywood cops had taken the same path as the murderous New York duo — doesn’t sit too well with the FBI.

***

Out there in Gang Land, many people on both sides of the law probably assume that the feds always go the extra mile whenever one of their own has been harmed.

Don’t try telling that to William Aronwald, a former federal prosecutor whose father was gunned down in 1987 by a trio of bumbling gangsters who mistook the father for the son in a mob hit.

This week, Mr. Aronwald ripped U.S. Attorney Roslynn Mauskopf of Brooklyn for what he called “unprofessional and irresponsible” conduct by her office in its dealings with former mob associate Frank Smith, one of the participants in the killing.

“Shame on the U.S. attorney’s office,” Mr. Aronwald said. “We’re the victims here, my family.”

In the past, Mr. Aronwald has criticized Ms. Mauskopf’s office for not pushing for tough sanctions initially against Smith, whose cooperation led to the conviction of Colombo underboss Joseph “Joe Waverly” Cacace, now serving a 20-year sentence for ordering the murder of the former prosecutor’s father.

More recently, Mr. Aronwald has condemned them for letting Smith off the hook when he was arrested in November for grand larceny, after a short, house arrest term. That arrest, for stealing a load of flat screen TVs, was a violation of the terms of the reduced sentence he received in the killing of Mr. Aronwald’s father.

Yesterday, Mr. Aronwald said he was even more irate that he had been kept in the dark that Smith had finally been charged with violating the terms of his sentence, and now faces up to three years in prison. Smith testified about that Tuesday, when he appeared on behalf of an old buddy, Carmine Carini, stating he was wrongly convicted of a 1983 murder.

Ms. Mauskopf, he said, had personally assured him that her office would keep him “in the loop” about Smith’s case.

But, the ex-prosecutor told Gang Land, he has been consistently been rebuked by the office, and only learned about Smith’s testimony in the Carini case after he was off the stand Tuesday. And the information, he said, came not from Ms. Mauskopf, but from a New York Post reporter, Alex Ginsberg.

“I would expect that someone from the government would have the courtesy to call me,” said an “extremely disappointed” Mr. Aronwald, who is now a defense attorney.

A Mauskopf spokesman said that “in light of pending court proceedings in this case,” the office would not respond to Mr. Aronwald’s remarks.

This column and other news of organized crime will appear today at ganglandnews.com.