How did Gollum escape from Moria ?

[Findegil]

I doubt that there was another entrance to Moria from the East beside the main doors that the fellowship used. The bridge of Moria would also be useless as a protection if there had been a second way around it.

But the destroyed bridge did not stop the orks from coming after the fellowship once the sun was down. I assume that they bridge the chasam as they had done before with the firefill trenches in the hall: Trolls bringing large stone plates.
And by the same way Gollum can have passed. There was no orc-guard on the brige when the fellowship arrived, so why should there be a guard on the new 'brige' after they escaped?

The doors seemed not to be guarded very well either. As already mentioned Gollum sliped in unseen once before and the Fellowship had no big problem fighting their way out.

We also have to consider that there passed about 6 hours between the escape of the Fellowship and the time when the orc pursuer followed them. That is certainly enough time to find some lazy moment of an Orc-guard to slip by unseen for Gollum.

Respectfully
Findegil