Get the HEV suit and activate the impulse 101, impulse 105, and notarget codes. Reactivate the cheat screen, and keep using the impulse 101 code until your HEV suit is full. Choose the high explosive (press 5 twice) and return to the lobby in Sector C Test Labs, where the security officer is on the computer. Go behind the desk and toss a high explosive under the desk. Walk anywhere you want, but not past the loading point, then detonate it. Walk back and the security officer should be on the desk. Talk to him.
After the scene where the experiment goes wrong, you will go through a series of transportations, etc. After that, you should end up in the experiment room. Exit both rooms and you will see a scientist performing CPR on a guard. Use the codes to get any human weapon and shoot the guard. The guard will say something along the lines of "You're gonna regret that".
Activate the impulse 101, impulse 105, and notarget codes and get the Magnum. Walk up to a scientist from behind, then shoot him in the back of the head. Certain ones will make a noise, stand for about ten seconds, then fall and die.