How does Sam Know?
 

When Faramir tells Sam and Frodo that Boromir is dead they are stunned because they were not there when Boromir took three arrows in the chest. Yet a few scenes later when Sam is pleading for Farmir to let him and Frodo go he blurts out the desire to take the ring killed him. How since neither Faramir nor Sam or Frodo knew the timing nor matter of Boromirs death did Sam now that Boromirs momnet of weakness led to his killing by orcs?

Are you referring to this quote?

TT The Window on the West

Later we have this also from Frodo:

TT The Forbidden Pool

In the first quote, Sam tells of his growing suspicion of Boromir's intentions leading up to the Breaking of the Fellowship, already knowing full well what he had done to Frodo before his death. That is before Faramir learned the truth about the errand of the Fellowship.
The second quote was spoken after, when Faramir, Frodo and Sam had discussed the event. I don't see the issue you speak of.
By the way, welcome to the Downs!

Inziladun, I'm guessing dasbill is talking about the equivalent scene in the film. In that version–

1. Faramir has already learned of the Ring (from Gollum) and is determined to take it

and

2. Sam does say:

"You want to know why your brother died? He tried to take the Ring from Frodo!"

So yes, there is an issue. Obviously it's just a bit of carelessness on the part of the screenwriters... for an in-story explanation, I suppose you could say Sam's just yelling random stuff in the heat of the moment.

Ah. I've only seen the movies once, and that years ago.
Thanks for the clarification, Nerwen.

But that scene is when Faramir is taking Frodo and Sam to Osgiliath. At that point the hobbits learned (through Faramir) that Boromir was dead. My guess is it was one of Sam's last ditch efforts to have Faramir let them go...Faramir is taking them to Osgiliath, claiming the Ring for Gondor, so Sam might as well try and say Boromir died because he went mad and tried to take the Ring because Sam's entire line is...

"You want to know why your brother died? He tried to take the Ring from Frodo! After swearing an oath to protect him. He tried to kill him! The Ring drove your brother mad."

As a mild criticism of the screenwriters: in the book, of course, Elrond explicitly says that no oath of any sort was laid on the Fellowship. And in the movie version, although one might reeeeeally stretch and claim that Aragorn's, Gimli's and Legolas' declarations to Frodo are 'oaths', all Boromir says is "If this is indeed the will of the Council, then Gondor will see it done."

I don't think in this instance the screenwriters altered the meaning of the text all that much. Obviously in the movies when all the companions pledge there support the dialogue is completely made up. And in the books The Council ends with Frodo saying he'll take the Ring and Sam jumping in. Later Elrond informs Frodo of his other companions and Merry and Pippin are the last two. All the screenwriters did was condense and have the entire Fellowship form during The Council of Elrond. I think it was necessary condensement to keep the movie going and the Fellowship out of Rivendell. For this to happen, yes dialogue had to be invented and it does look like some companions pledge an oath to Frodo.

But, I find Elrond's choice of words, regarding any oath on the Fellowship important:

There is no oath on how long, or far, anyone on the Fellowship needs to stay with Frodo. Elrond does make it clear that the members are free, they can leave Frodo at anytime. However, right before the quote above Elrond says:
Only in the gravest need is anyone of the Company allowed to handle the Ring, and this is of course at Frodo's discretion. There may not have been any sworn oaths, or 'swords,' as shown in the movies but there were conditions to being a member of the Fellowship. That is only Frodo can handle the ring, unless he lets another member if need calls for it, and the company is to help Frodo on his way. Boromir broke the second. Now whether he broke a sworn oath or not, I don't know. But I will ask what did Boromir need forgiveness from if he was completely free and not bound by any oath while in the Fellowship?

There were far worse diversions from the script than the scenes being discussed. Yes the dialogue is completely made up, but the condensing of forming the Fellowship during The Council can be argued as being necessary. While no oath was placed on how long someone decided to stay in the Fellowship, that doesn't mean there were no bonds at all. There may not have been an explicit oath, but Frodo's 'charge' was to bear the Ring to it's destruction and I think it can be implied the Fellowship's duty was to help him on his quest. Boromir broke these when he tried to take the Ring by force.

I think Boromir's need for forgiveness is bound to his nature. Faramir exhibits the type of behavior we all wish we would when faced with the ring (in the book), but Boromir doesn't.

Boromir thinks like a commander of Gondor's army would have to think - that any weapon should be used against the enemy - but he is a just, honorable man. His need for forgiveness comes after the ring has left and he can see what it has cost and what it might cost. While we know that everything turns out all right, there was no reason for Boromir to think that two little hobbits could find their way into Moria and destroy the ring by thereselves. He might not only have failed himself but doomed the whole of Middle Earth. Also even if no oath was laid upon them, Boromir may still have considered it his duty to protect the company, for what has he been doing his whole life but protecting other people as a soldier.

Do you mean Mordor?
Also, in the book, when the Fellowship members hold their own counsil just before leaving Lothlorien, Boromir thinks aloud and says things that suggest that he wants to use the Ring as Gondor's weapon against Sauron. Although Sam was sleepy at the time, he could have heard and remembered the words, like he overheard Frodo's and Gildor's conversation in the Shire.