Presumably Yu Aida is finalizing plans for something tragic because the Gunslinger Girl manga is set to end by the close of 2012. According to Mangaoh, the 2002 series about traumatized girls turned into special ops assassins will end in its 15th volume, slated to ship in Japan on Decamber 17th. A limited edition will be packaged with a mini-art book.
This means that the manga is likely to wrap up serialization in the December issue of the Monthly Dengeki Daioh anthology, which goes on sale October 27th.
The manga series was adapted into anime in 2003 and 2008, and both were released in North America by FUNimation. It also aired on the IFC cable network. Seven Seas picked up the manga after the end the demise of ADV's line.