Not only he hints about Anderson, but he also raises questions about Saren´s past.
You can go to the C-sec boss trying to find garrus, but he won´t mention anything regarding the investigation.
It may be possible that Garrus was investigating on his own, since his boss told him that the case was closed for him. Anyway, one interesting thing is that should you go to barla von instead and recruit wrex, you can skip meeting garrus at the clinic, as well as never interacting with Harkin. So it´s garrus that will request to join you when you´re about to leave the citadel. If you do not speak to harkin, in me2 he will not recognize you.