Michael arranges to have Roth killed at the airport where he is about to be taken into U.S. federal custody. Minutes after disembarking the plane, he is fatally shot by Michael's caporegime Rocco Lampone, posing as a reporter. Rocco himself is killed by federal agents as he tries to escape.
It was unknown if Michael sending Rocco after Roth was to punish him for his previous failure by sending him to his death, or so that he could redeem himself in Mochael's eyes. If I had to guess it was probably both. Regardless, Rocco succeeded in killing Roth, and died loyal to Michael.
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.
Fredo was aware that Hyman was angry with Michael's aggressiveness in Las Vegas, and he simply allowed Hyman to attempt to kill Michael so that he could hopefully claim the title of Don Corleone. Of course, we all know how it eventually ended up going down.
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.
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.
Eventually Vito splits Tessio from Clemenza and asks the two not to socialize unless absolutely necessary, both to remove the threat of a conspiracy against him and also to set up Tessio to function as a "safety valve caporegime" whose Mafia soldiers can be called upon by the Corleone family in emergencies.
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.
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.
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.
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).
Fredo's decision is most likely a result of resentment toward Michael, by whom he felt he had been passed over. Michael was Fredo's "kid brother," and the fact that their father chose for Michael to take over the "family business" came as a great insult to Fredo, who was neither as intelligent nor as strong.
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.
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. Michael quickly realizes that Roth ordered the hit.
Betrayal. While in Havana, Michael learned that Fredo betrayed him when Fredo accidentally let it slip that he and Johnny Ola had been to a sex show in Havana. He confronted Fredo at a New Year's party in Havana, telling Fredo that he knew he was the traitor and giving him the "kiss of death".
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.
In the late summer of 1948, Sonny Corleone was lured into a trap and was killed at the Jones Beach Causeway by Barzini family hitmen in order to avenge Carlo. The hit was engineered by Emilio Barzini after Carlo, angered at the loss of his income and at the fact that Sonny had beaten him, helped set it up.
Soon, the Rosato Brothers supposedly killed Frank Pentangeli, faking their service to Corleone in order to convince Frank, one of the Corleone's most long-time supporters, to give up his allegiance. It was not long until he filed an offense against Michael Corleone in court.
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 was scheduled to return in The Godfather Part II, but due to a disagreement between Castellano and Paramount, his character was killed off and was replaced by Frank Pentangeli.
