I noticed a user on SO who seems to be copying and pasting answers from other sites without any attribution and presenting these as his own work. Presumably he's just doing this to build up rep. I've flagged a few of these plagiarised answers but I'm wondering if there is anything further I should do ?
Use a moderator flag with a custom reason and explain that there is a pattern of misbehaviour, if you haven't done so. This will lead to the moderators investigating the user's history, not just the specific flagged content.
In cases where there is a problematic user behaviour that is not apparent from just seeing one post, it's always a good idea to add some detail in the flag reason.