Pronoun?

[Unregistered]

Is the following sentence grammatically correct - i wonder if there should be a pronoun (HE) between the words SO and KNEW

"It was written by Lewis, a journalist who had spent a lot of time in London, so knew what he was talking about"

 

[David L.]

"It was written by Lewis, a journalist who had spent a lot of time in London, and so knew what he was talking about."

 

[Uncle M]

Or

It was written by Lewis, a journalist who, having spent a lot of time in London, knew what he was talking about.