The campus security guard's position after being killed changes from one shot to another. When he's killed, he falls to a laying position with just his head propped up to the door. When the camera cuts back to him after 33 seconds, he is now in a sitting position with his back propped to the door.
After being shot multiple times, the high school campus security guard falls to the ground where he dies. As he lay there, we can clearly see the Squib wiring that is used for the effect of being shot. It's lined through his left leg and protruding from his uniform pants.
When the reporters are questioning Chief Slater when he initially pulls up to the school, none of the microphones they are using are connected to anything. The microphones are clearly ones that require a wire connection to a recording device.
When Chief Slater dials the terrorists, he uses a cell phone to call into the school. When the terrorist is making his demands, he is speaking not only to the chief, but to two FBI agents at the same time, all on individual cell phones. It is impossible to conference call three different cell phones at once, unless the Chief dialed one FBI agent, that agent dialed the other FBI agent, and the last agent dialed into the school.