weapon that investigators had been looking for. >> one was inoperable. the other 9 millimeter handgun was test-fired into a tank of water. that bullet was microscopically compared to the 9 millimeter slug found in the van dusens' jeep. analyst erica henderson carefully examined the distinctive marks called lands and grooves made when each bullet goes through the barrel of the gun. >> when you look down the barrel of a firearm, you will see the ridges and valleys. these ridges and valleys, once a bullet is fired, will be imparted on the bullet. so the bullet will also have these ridges and valleys. >> the test bullet and the one from the crime scene were turned repeatedly as henderson checked and rechecked the markings. but the results showed that henry sullivan's gun was not the murder weapon.