How did Gollum escape from Moria ?

[Legate of Amon Lanc]

Originally Posted by The Mouth of Sauron

Gollum started following the Fellowship after they entered Moria at the West Gate. And throughout the journey through Moria, both Frodo and Aragorn (and almost certainly Gandalf too) were aware of his presence.

But considering Gollum was FOLLOWING, how did he cross the chasm which the Bridge of Khazad-Dum had spanned ? The Fellowship were the last to cross the bridge before Gandalf destroyed it. And yet Gollum was right behind the Fellowship, on the borders of Lorien, only hours later.

Is there anything on this matter by Tolkien? (Letters, something... I would think that somebody might have asked him about that.) Anyway, if I were to state my opinion, what comes on my mind right now is that Gollum actually managed to cross the Bridge BEFORE the Fellowship - when the matters got nasty, perhaps he was forced to move eastwards (because the Orcs were approaching from the West) and then crossed the bridge and went outside, or something like that. Though, there were still the guards... I guess Gollum must have (in any case) used the chaos created by the Fellowship's coming to sneak out.

Also, didn't the Orcs cross the pit after the destruction of the Bridge, too? Wasn't there some other way (apart from the one Gandalf and Balrog took, that is)? Perhaps Gollum could cross that way. Though he certainly had to be quick, as he was seen by Frodo almost that very night.