Michael kills Sol and McCluskey because he and Sonny want him dead, and because Michael thinks that the "key" for Sol is to "kill Pop." My question is "How?" Strike one was that the hit men did not kill him when he was at his most vulnerable. Strike two was when McCluskey called off his guards at the hospital but was thwarted by Michael and Hagen's legal maneuvering. After that Vito returned to his Mall, and he was too sick to be out in public all of the time. In fact the only times ever was seen to leave the mall again was when he went to Bonasera's funeral home and when he went to make the deal to sell drugs and bring Michael home. Otherwise he would have been under very tight security, and other than getting someone inside the family to do it a' la the drapes in II, how would Sol have killed him?
As Sol himself said, " I missed my chance."

DT, it wasn't until February 1946 that Vito was moved from the hospital to the Mall. If the attempt on Vito took place in December, Sollozzo would have had several weeks at least to attempt another murder. Keep in mind that after Vito was admitted to the hospital, Sonny didn't know how long he would have to be there.

Yes but didn't the armed guards they got make it impossible to penetrate the hospital? I mean they would have to screen all the nurses, doctors and even the meds given to Vito, but with security that tight I wonder if Barzini wold tel Sol to back off.

No way,no how, is Sol going to get a chance to hit Vito in the hospital. Between the "private detectives" and the Corleone guys,any unusual activity is going to be noticed and dealt with immediately. Any ripple in the normal routine,any new face on the staff,the newspaper coming five minutes late,any thing out of place would shut the place up tight as a vault.

Having said that,Sollozzo may have been successful using unconventional means.Let's say that he had a contact who could have poisoned Vito's food while it was being made,or an employee who would go on the take to spike Vito's IV bottle.

If he didn't get killed in the hospital,I agree that Vito would not have been an easy target once he got home,and Sol would not have had another crack at him.

As Michael opined after returning from the hospital: "And with that police captain helping him who knows what the hell might happen. We can't take that chance."

It was a matter of life and death for Sol--every day, a hundred of Sonny's button men were on the streets hunting for him. The clock was ticking. Sol would have tried anything--anything at all--to kill Vito, even if it came to bribing or coercing someone on the medical staff of the hospital to poison Vito before he could be moved to the mall.

I am convinced Oli and TB are right on this one, which would mean that Sonny and Michael were right as well. Given that when you watch the scene play out, it is Sonny who first tells Tom he wants Sol dead, and it is Tom who taks him out of it, in order to "patch things up." It is only when Tom prevails on Sonny and Sonny says, "I'll wait," does Michael speak up. His approach is very cold blooded, and very well reasoned. He gets Tom on board by selling him the idea that they can get newspaper people on the payroll to smear McCluskey and minimize the murder of a police captain. Then after Sonny mocks him, Michael convinves him be coldly telling him "Its not personal. Its business." It is at that moment that Michael becomes the de facto head of the family.

I always figured that it meant not immediately, but if Sollozzo was allowed to live he would make peace and then later finish the job.

I think it's perfectly clear that Sollozzo is still going to try to have Vito killed one way or another during the restaurant chat between him and Michael.When Michael says that he wants a guarantee that there will be no more attempts on his father's life,Sollozzo says that he can't give one and only wants a truce.This was the key part of the whole discussion----it confirms beyond a shadow of a doubt Michael's belief that Sollozzo was never going to stop trying to eliminate Vito until he was unable to do so----A.K.A. HE'S DEAD !!!! I know Sollozzo goes into that whole spiel about being the hunted one,missing his chance,etcetera,but his initial reflexive answer revealed the truth.Michael even shows a slight hint of recognition(great acting,Al)upon hearing this.The conversation is over at this point and Michael is determined to get it over with as quickly as possible.