"The Truth About Halo, Part 1 of 4: Goodbyes"
Continues in Batman and the Outsiders (Vol 1) #20.
Tatsu a.k.a Katna is amazed when she finds that Batman has been working on finding out Halo's true identity. Between detective work done by himself and Jason Bard, they have put together bit's and pieces of information that have lead them to Halo's parents.