-ing & -ed clauses

1.Which one is correct? and why?
Inspector learned that all the murdered men [color=darkred]worked/working as bankers.

2.I should join these sentences.

He’s an art collector.He knows a lot about precious stone.

my answers:
[color=olive] a.He’s an art collector knowing a lot about precious stone.
[color=blue]b.He’s an art collector who knows a lot about precious stone.

Could both sentences be correct?

Thanks in advance

The Inspector learned that all the murdered men had worked as bankers.

  1. B is the correct version, but ‘stone’ should be plural - ‘stones’.

Thank Beeesneees

Could you explain why A is not correct?

another question :

Can stative verbs be used as a present participle meaning adjective?

At the very least it would need a comma to indicate a clause containing additional information.
He’s an art collector, knowing about precious stone.
But even then the context is such that the whole structure sounds really odd.