This is a cite from Wikipedia that explains how Ragano is not credible:

On January 14, 1992, Ragano told Jack Newfield of the New York Post that he relayed a request from Hoffa to Trafficante and Marcello asking that the two Mafia bosses kill Kennedy.[33] He repeated the claim two days later on ABC's Good Morning America,[34] in Newfield's Frontline report entitled JFK, Hoffa and Mob broadcast in November 1992,[35] and again in his 1994 autobiography Mob Lawyer.[28]

According to Ragano, he met Hoffa at the Teamsters' headquarters in Washington D.C. then delivered the message to Trafficante and Marcello a few days later in a meeting at the Royal Orleans Hotel in New Orleans.[33][34] He stated he was chosen by Hoffa because, as both Hoffa and Trafficante's lawyer, he could be assured of attorney–client privilege.[33] Ragano said that Jim Garrison served as a patsy for the New Orleans mob by disseminating theories that served to distract attention from mafia figures who were involved in the plot.[36]

Although Ragano believed he had received a few hints from both Trafficante and Marcello that they had somehow been involved in the Kennedy assassination, it was not until just before he died in 1987 that Trafficante, according to Ragano, made a direct confession to him. Ragano wrote that on March 13, 1987, a dying Trafficante (he died four days later) asked to meet him in Tampa for a hurried meeting. While riding in Ragano's car, Trafficante allegedly told Ragano in Sicilian: "Carlos e' futtutu. Non duvevamu ammazzari a Giovanni. Duvevamu ammazzari a Bobby," which Ragano translated as: "Carlos screwed up. We shouldn't have killed John. We should have killed Bobby."[37]

This was later found to be a complete fabrication by Ragano, because hospital records proved that Trafficante was in Miami receiving dialysis several times that week. The day that Ragano claimed to have talked to him was one of the days he was actually receiving dialysis. Hospital personnel, neighbors, and friends who all visited the afternoon before he left for Houston from Miami could also confirm this. The evening before leaving for Houston, because of his weakened condition, Mr. Trafficante was driven to the Miami airport by his goddaughter, so that she could help Mrs. Trafficante with securing a wheelchair and other boarding procedures.

This claim by Ragano, seemingly pointing to a successful mob plot to assassinate JFK, has come under much criticism. In his book Reclaiming History: the Assassination of President John F. Kennedy, Vincent Bugliosi has pointed out many flaws in Ragano's claims, including the fact that Trafficante was most likely not in Tampa on the day in question, but was rather in North Miami Beach receiving dialysis treatments.[38]

Bugliosi based much of his conclusions on the research of author Anthony Summers. Summers reviewed medical records and talked to Trafficante's family, neighbors and friends, and discounted the idea that Trafficante could have been in Tampa on the day in question. When Summers talked to Ragano about these problems, Ragano told Summers that he could produce three witnesses who could prove his story, but never did so.[39]

Both Trafficante and Marcello were very private individuals. The House Select Committee on Assassinations in its 1978 Final Report noted specifically that Trafficante was a very "discreet" individual who was unlikely to have made such an admission.[40] Bugliosi argues that it is absurd to think that Marcello and Trafficante would get involved in plotting to assassinate a president, particularly as nothing more than a supposed favor to Jimmy Hoffa.[41] Bugliosi also points out that by allegedly conveying a message in 1963 to that effect, and by relating this confession from an alleged conspirator, Ragano would himself be admitting to having been a part of a murder conspiracy.[42]

Shortly after the intial allegations, Jeffrey Hart compared Ragano's account with that presented in Oliver Stone's recently released film JFK.[43] According to Hart, Ragano presented an "earthy motive, vastly more plausible than the movie theory."[43] Hart quoted G. Robert Blakey as stating that he believed Ragano and that his testimony "would have strengthened the conclusions" of the HSCA.[43] Hart also quoted Frank Mankiewicz, Robert Kennedy's press secretary, as finding Ragano's scenario as "the most plausible (assassination) theory".[43]

When Ragano was questioned by the Assassination Records Review Board, created in 1992 to reexamine JFK conspiracy theories after the release of Stone's film, he claimed to have contemporaneous notes of his conversations regarding the JFK plot, but when they were produced, "he could not definitively state whether the notes were taken during the meetings [with mob figures]... or later when he was working on his book." His notes were subjected to Secret Service tests to determine when they were actually prepared, but the results were inconclusive.[44]