In the episode Euphoria (Part 1), Officer Joe Luria was chasing him due to the fact that he was a suspect in something that Luria was investigating at the time. Luria chased him around a neighbourhood. He hid in a dumpster but Luria knew that he was there. Luria told him to come out with his hands on his head, Brian came out but his hands weren't on his head, he told Luria that it was impossible to come out of a dumpster with his hands up. luria told him to pull up his collar, his did which revealed a gun Luria suddenly started acting really strange and cracking multiple jokes Brian asked if he was high but he continued to joke around about arresting Luria offended his mother and he pulled out a gun and shot Luria. The bullet hit Luria's bulletproof vest and shattered. One of the bullet fragments went into his brain. Luria fell on the ground and started bleeding. Yet strangly he continued laughing even after being injured.
Brian was caught (possibly by Luria's partner). He was brought to either the hospital or the police station where he was questioned about what happened to Luria before getting shot. Among other things he told them that he was euphoric previous to being shot in the brain, this eliminated brain damage as a possibility of a cause of the euphoria. Foreman wondered whether or not Brian was actually a reliable wittness. House thought that he could be a reliable witness due to his name (he was kidding). They trusted the information that he gave and eliminated brain damage.
He uses ferromagnetic bullets, this is revealed when the team was wondering about whether or not they could do an MRI on Luria. Foreman informed House that Luria's bullet-proof vest would not shatter the bullet, it would catch it instead, meaning that the bullet shattered on its own. The type of bullet that does this is made of ferromagnetic materials, and as such would be ripped out during an MRI.