Vito was betrayed by his driver Paulie Gatto who called in sick the day Vito was shot. Paulie knew that it was more than likely that Fredo, who was imcompetent at defending his father and handling firearms, would be Vito's driver/bodyguard that day.
When Corleone refused, Sollozzo had Bruno Tattaglia murder Luca Brasi, Vito's most trusted enforcer, and put a hit out on the Don, which resulted in Vito's wounding.
Ultimately, Tessio betrays Michael by helping arrange his assassination at a peace summit with Barzini and Philip Tattaglia. The summit will be held in Tessio's fiefdom in Brooklyn, where Michael will presumably be safe. In return, Tessio was to inherit the Corleone family upon Michael's death.
Fredo betrayed his brother to rival gangster Hyman Roth, who used him as a pawn in a plot to destroy the Corleone Family. Fredo provided unspecified information on the Corleone family in return for receiving compensation (what kind is never specified) independently of the family.
6 Salvatore Tessio Betrayed Michael So He Could Take Over The Corleone Family. Before Vito passes away, he tells Michael that the man who has betrayed him will approach Michael and try to organize a sit down between him and Barzini.
How did Vito Corleone know Tessio was the Traitor? Why Did Tessio Betray Michael Corleone?
Who kills Clemenza?
Most noteworthy, the novel depicts Clemenza's fatal heart attack (mentioned in The Godfather Part II), and the many conspiracy theories that he had actually been murdered by the Rosato Brothers, former Corleone soldiers who had formed their own gang after a dispute over the future of the family.
Vito above all knew people and also how to survive in his profession. So he knew that who ever came to Michael with the offer to meet with Barzini was the traitor in the family. That would turn out to be Tessio.
He is also mentioned many times throughout the film; the dialogue makes it clear that Michael is tormented with guilt over ordering his brother's death, and that it has alienated him from his ex-wife, Kay (Diane Keaton), and his son, Anthony (Franc D'Ambrosio), both of whom know the truth about Fredo's death.
A rift grows between Pentangeli and Michael, however, that eventually results in Pentangeli betraying the family. Pentangeli's character was created in The Godfather Part II by Coppola and Puzo due to actor Richard Castellano not reprising his role as Clemenza in the sequel.
Roth secretly plans to assassinate Michael, partly to avenge Moe Greene's murder (as depicted in The Godfather). Roth instructs Ola to befriend Michael's brother Fredo, who provides Ola (and Roth) information about Michael that enables them to make an attempt on his life.
Emilio "The Wolf" Barzini is a fictional character and the main antagonist in Mario Puzo's 1969 novel The Godfather and in its 1972 film adaptation, in which he is portrayed by Richard Conte. The Barzini crime family was inspired by the Genovese crime family.
After her brother's debut concert, the assassin Mosca tries to kill Michael. One bullet grazes Michael's shoulder, but the other accidentally hits Mary in the chest, fatally wounding her. Michael is devastated by Mary's death, and screams in torment while cradling her dead body.
When Hagen's longtime mistress, Judy Buchanan, is murdered by thugs working for Don Carlo Tramonti, Hagen becomes a person of interest in the investigation, though he is later cleared of the charges. In August 1964, Geraci kidnaps Hagen and drowns him in the Florida Everglades.
Fredo would have been exiled to a position of no control whatsoever and “managed” for the rest of his natural life. Sonny and Vito would have kept him alive, in a role where he could not hurt them. They would let him live out his days fishing in the compound.
Paulie has seemingly betrayed Vito—and thus the family—by selling him out. In The Godfather, this kind of betrayal is the worst of all sins. We see the matter discussed, in the Corleone family office, just before the viewer spends time in front of Clemenza's cozy abode.
Vito is seriously wounded in the attempt. Having Paulie brought to the Corleone compound Sonny Corleone deduced that Gatto had sold out his father. Sonny ordered Clemenza to have Gatto killed as soon as possible, saying he did not want to see Gatto again.
Roth arrives at the airport and prepares to be taken into Federal Custody in the U.S. Minutes after getting off the plane, he is shot point-blank by Corleone caporegime Rocco Lampone, who was posing as a reporter. Rocco was then shot and killed by federal officers as he was running away.
Enraged, Sonny speeds towards Connie's apartment in Hell's Kitchen ahead of his bodyguards. At the Long Beach Causeway toll plaza, Barzini's men trap Sonny and shoot him to death. During a meeting with the other crime family dons to establish peace, Vito realizes that Barzini masterminded Sonny's murder.
In the novel, Greene is murdered shortly afterward by Al Neri. At the end of the film, Michael has Greene killed as part of his slaughter of the Corleone family's enemies. Neri surprises Greene while he is getting a massage and shoots him through the eye.
As Fredo prays the Hail Mary (which he claimed brought him luck whilst fishing), Neri shoots him in the back of the head, not knowing that Anthony was watching from his bedroom window.
So (because this is getting lengthy), I'll end it here: Why did Hyman Roth give the order to kill Frank Pentangeli? Because he needed a snitch to testify against Corleone. What advantage would that give him? Roth's intention was to put Corleone away for life (since he couldn't kill him).
The third and final film in the Godfather saga, The Godfather: Part III, set in 1979, explains that Hagen had died a few years earlier. His son, Andrew, is ordained to the priesthood, and is assigned to the Vatican on Michael's recommendation. While talking with Andrew, Michael remembers Hagen fondly as a great lawyer.
Willie Cicci and a few other men drove Tessio to Two Toms, his social club, where his traitorous men were executed. Tessio, and his dead co-conspirators were then brought to an abandoned gas station on Staten Island where he was executed by his former protege Nick Geraci, while Al Neri looked on.
In a fit of pique, Carlo sought revenge by making a deal with the Corleones' rival Emilio Barzini to kill Sonny, which would break the stalemate of the Five Families War and possibly allow the other crime families to negotiate a deal to sell narcotics in Corleone territory.
Clemenza remained loyal, and personally assassinated Victor Stracci with a gunshot as he was coming out of an elevator during Michael Rizzi's baptism. He also garroted Carlo Rizzi, Connie Corleone's husband, in revenge for Carlo's purported involvement in the murder of her brother Sonny.
