What’s the US military’s investigation on?

The US military has opened a criminal investigation into the death of two New York State National Guard officers at a base in Iraq.
   The initial US military investigation indicated Captain Philip E and First Lieutenant Louis Allen were in the same room when a mortar round hit the room’s window. The subsequent explosion was thought to have killed both soldiers. But a military explosives team determined the blast was not caused by a mortar. A criminal investigation would indicate that this explosion was caused by negligence or sabotage, not by enemy fire. Captain E was company commander of the Headquarters Company of the New York National Guard. The Guard is part of the 42nd infantry division based near Saddam Hussein’s hometown of Tikrit. Lieutenant Louis was operations manager for the company.