3 Good evening. Tonight we're learning much more about the school shooting in Centennial, Colorado ...including the name of the shooter-- who he was targeting, and why. It started shortly after lunch ... senior Karl Pierson stormed into Arapahoe High School..just 8 miles from Columbine High, armed with a shotgun and two molotov cocktails. Police say he shot and wounded one student... the 15 year old girl is in serious condition... Authorities say he then killed himself. Originally, police thought another girl had minor injuries, but we're told she was NOT wounded...the Sheriff says she thought she was hurt because she had blood on her, but it was actually the 15- year-old's. Sources say Pierson was targeting librarian Tracy Murphy who also worked as the speech and debate team coach. Sources say Murphy benched Pierson from the debate team just days before. When Murphy heard he was the target, he left the campus. A school janitor says he saw Pierson running down the hall in military style clothing. 3 3 3 he was kinda running, side to side....looking for one person. BUTTED We heard, you know, it was just a really big bang...We're all scared now. The shooter is dead and a 15 year old girl has been downgraded to critical condition after surgery... About an hour ago, we learned that Karl Pierson, a senior at the school, was the shooter. He was described as being 'geeky' and 'sweet.' Channel 4's Scott johnson has been following this... He spoke with our Crime and Safety Analyst about how police handle such a traumatic event..Scott? 3 12-1829-34 they were marched out single file with their hands raised... these were the students of Arapahoe High School.SHERIFF GRAYSON ROBINSON 20:01:25 - we evacuated the school quickly and deliberately while we were evacuating the school, no staff or students were injured. And that's a marked comment because the evacuation was done in a thoughtful and deliberate manner.and channel 4 crime analyst ken jefferson says the manner the sheriff in arapahoe county colorado spoke of is exactly what needed to be done. KEN JEFFERSON 10:56 - you must do this in a situation like this. You've got an active shooter, don't know if in buidling and still around. Don't know if he has an accomplice.So it's imperative that police gain order and get people out of building.the students were each searched as they were taken out of the building... and while that process took a long time... the shooting did not. Investigators say the ssuspect shot two students and even deployed a molotov cocktail. They suspect he wanted revenge on a teacher.SHERIFF GRAYSON ROBINSON 20:00:36 - I believe the shooter knew that deputy sheriff's were immediately about to engage them and I believe that shooter took his life because he knew that he had been found.ken points out the response of police was overwhelming to this school of thousands.He says SWAT officers train to go into buildings like these regularly... which is exactly what they did as they searched initially for this shooter... and then for any potential accomplices.KJ 15:32 - swat teams all over country train for something like this.They go room by room and search every nook and cranny of that building. So right now investigators have three scenes away from the school. One is the suspect's car...another his house...and the third is a house he had some sort of access to. All those are being searched and processed now to find out why he went to the school and if he acted alone. 3 Scott, were students and staff allowed to return to the school since this happened early today?