Fort Hood, Texas (CNN) -- Crime-scene testimony dominated Tuesday's proceedings in the court-martial of admitted Fort Hood gunman Nidal Hasan, with an FBI agent describing the "chaotic" scene of the 2009 massacre.
Special Agent Susan Martin, a member of the team that collected evidence from the processing center where Hasan is accused of killing 13 people and wounding 32, said seven bodies were visible from the moment she walked in the door.
The yellow folding cards, known as "tents," that agents carried to mark evidence numbered only up to 100 -- a figure far short of the number of shell casings and bullet holes investigators had to catalog, she said.
"It was very chaotic," Martin said. "There were several bodies in Area Four. There was medical equipment all over the floor. It was a pretty gruesome scene."
Investigators had to use adhesive-backed pieces of note paper to identify the evidence scattered across the floor, she said. The FBI ultimately entered 146 shell casings and six magazines into evidence from the scene.
FBI Special Agent Brett Mills analyzed the trajectory of 58 of the bullets from five separate shooting locations, calling it "the worst scene I've ever seen."
Agents analyzed the trajectory analysis of more than 270 bullet holes in the building, but could not re-create all of the paths of the bullets because furniture and other evidence was moved in the process of trying to treat victims, they said.
Hasan, an Army psychiatrist who was paralyzed by a police bullet during the rampage, admitted at the start of the trial August 6 that he opened fire in the processing center where soldiers were being prepared for deployment to Afghanistan and Iraq.
A U.S.-born citizen of Palestinian descent, Hasan had been scheduled to deploy to Afghanistan before the killings.
Prosecutors allege the devout Muslim had undergone a "progressive radicalization," giving presentations in defense of suicide bombings and about soldiers conflicted between military service and their religion when such conflicts result in crime.
If convicted, he could face the death penalty. In a military capital trial, a guilty plea is not an option.
Hasan is representing himself, but with attorneys assigned as stand-by counsel to assist him. Those lawyers requested to be removed last week, saying they believed Hasan was trying to help prosecutors win a death sentence.
The presiding judge, Col. Tara Osborn, refused their request Thursday, calling their complaints "nothing more than their disagreement with Hasan's strategy in conducting his defense."
CNN's Matt Smith contributed to this report.