Conversation so far:
What was Dragnet about?
A pilot telefilm, based on the Harvey Glatman serial killings.
What role did Jack Webb play in Dragnet?
Joe Friday.
What did Joe Friday do in Dragnet?
Don Dubbins, who had acted alongside Webb.
Was Dragnet a cop show?
CANNOTANSWER.

Question: How long did Jack Webb act in Dragnet?
Self-contained rewrite: How long did Jack Webb act in Dragnet?