[William Cloud Hicklin]

I would add Boromir's statement at the council:

[Elrond:]'...and Isildur cut the Ring from his hand with the hilt-shard of his father's sword, and took it for his own.'

At this the stranger, Boromir, broke in. 'So that is what became of the Ring!' he cried. 'If ever such a tale was told in the South, it has long been forgotten. I have heard of the Great Ring of him that we do not name; but we believed that it perished from the world in the ruin of his first realm. Isildur took it! That is tidings indeed!'.......

[Elrond:]'Only to the North did these tidings come, and only to a few. Small wonder is it that you have not heard them, Boromir. From the ruin of the Gladden Fields, where Isildur perished, three men only came ever back....'

And after the Halfling, the Sword, and the Bane have been revealed, he says:

'I was not sent to beg any boon, but to seek only the meaning of a riddle,' answered Boromir proudly. 'Yet we are hard pressed, and the Sword of Elendil would be a help beyond our hope'

And Gandalf:

'And Boromir, there lies in Minas Tirith still, unread, I guess, by any save Saruman and myself since the kings failed, a scroll that Isildur made himself.

Certainly no news could possibly have reached Denethor about the Ring having been found or being in the possession of a Hobbit: indeed it was a secret known only to Gandalf, Frodo, Elrond and Aragorn in full prior to the Council. Bilbo and his Dwarven friends knew he had *a* Ring, which was not the same as *the* Ring; Sauron himself only got wind of it by torturing Gollum, of whom of course Denethor knew nothing; and Saruman was just beginning to guess at the time Boromir departed. In short, Denethor was as ignorant as Boromir of the Ring's existence, until Gandalf told him personally on the eve of the Siege.