When the officer walked out to speak with him, Kammeyer pulled a gun and pointed it at the officer and employee working behind the desk.
Police said Kammeyer kept the gun trained on them, even as the officer ducked back behind the desk and called for assistance.
Conger came down the stairs and opened the stairwell door, but quickly ducked back inside when he saw Kammeyer point the gun at Conger's head, according to a statement from the district attorney's office.
Conger kept the door to the lobby open slightly and stuck his gun through the opening and fired four to six shots, some of which struck Kammeyer.
A search warrant released prior to Monday's decision said Kammeyer's gun was unloaded, but his wife believed that Kammeyer wanted someone to kill him "because he didn't have the guts to do it himself."
Kammeyer, 39, is facing charges of threat of terrorism, three counts of aggravated assault and use of a firearm by a restricted person, all third degree felonies, in 3rd District Court.
He also has been charged federally with possessing child pornography.