CENTENNIAL, Colo. - The Arapahoe High School shooter entered the school through a door that should have been closed and locked, but was left ajar, Arapahoe County Sheriff Grayson Robinson said.
Robinson and several other law enforcement leaders held a news conference Monday to update the public on the investigation into the Arapahoe High School shooting on Dec. 13. That shooting left two people dead, student Claire Davis and the gunman, another student.
During the news conference, Robinson said the gunman, who he called the "murderer," but never identified by name, entered the school armed with a shotgun, a machete, 125-rounds of shotgun ammunition and three homemade explosives.
"[He] made no effort to conceal the fact that he was armed," Robinson said. "His intent was to use as many of those rounds as he possibly could and use the Molotov cocktails in the most destructive manner that he was able to do."
Robinson said the gunman entered the school on the north side. Robinson said the door is supposed to be locked.
"Unfortunately it rarely is, because it is more convenient for people to come and go from that area and not have to be obstructed by a locked door," Robinson said. "The door that he entered was not secured on December 13th. He entered without any obstructions."
When asked later in the news conference whether it would have made any difference had the door been locked, Robinson replied, "I don't believe it would have."
Robinson said the murderer fired six rounds.
"[He] came into the school and immediately fired one round randomly down a hallway," Robinson said. "His second round was fired directly at Claire Davis. A round that proved to be fatal."
The third round was fired down the hallway that went to the library/media center.
Robinson said the murderer then walked into the library. There he fired a fourth shot toward the office of the school librarian and speech coach.
"Then [he] went to central portion of the library and ignited a Molotov cocktail," Robinson explained.
Robinson said the explosion burned four book shelves and created a large amount of smoke and fire which initiated the fire alarm in the school.
Robinson said the gunman fired a fifth round, then went to the back portion of the school and used his sixth shot to take his own life.
Robinson said from the time the gunman walked into the school to when he killed himself, less than 80 seconds had elapsed.
-- No accomplice or co-conspirator found yet
Robinson said, so far, investigators believe the murderer acted alone.
"It is our belief that the murderer planned the tragic events of December 13 on his own and he executed his evil plan on his own," Robinson said.
When asked if the gunman was on school grounds lawfully, or if he had been suspended or expelled, Robinson said he was attending classes.
Robinson said investigators have conducted 200 individual interviews and the investigation is continuing.
The sheriff said the gunman bought the gun legally on Dec. 6. Robinson said the local store that sold the shotgun conducted an appropriate background check.
Robinson said the murderer purchased ammunition from Dec. 6 to the morning of the shooting on Dec. 13. Robinson said in addition to buying ammunition on the morning of Dec. 13, the gunman also went bowling by himself.
-- Shooting motive
Sheriff Robinson said investigators still believe the motive for the shooting was a disagreement between the killer and the speech coach.
Robinson confirmed a threat was made in September, however, Robinson said, it is "still part of an ongoing investigation to determine the exact content of that threat and how it was dealt with."
He did not release any other details.
-- Claire Davis remembered
Robinson talked at length about the victim.
He said, "Claire Davis was a 17-year old student at Arapahoe High School who was murdered. We know a lot about Claire Davis that, frankly, I wish we had never learned."
He said there are some people in your life that leave an impact on you and that "Claire left an impact on my life and on the lives of this community."
He also described Claire's parents as "people of purpose and people of principle. They are people who made a difference."
Robinson said there has been a lot of discussion about Davis being in the wrong place at the wrong time.
"I will tell you that on Dec. 13, 2013 shortly after 12:30 p.m., Claire Davis was exactly where she had the right to be. Claire Davis was at her school... engaged in the responsibility and process of preparing herself for her future," the sheriff said.
-- Security guard, sheriff's deputy were heroes
During the news conference on Monday, the sheriff pointed out the life-saving actions of the school resource officer, Deputy James Englert, and an unarmed school security guard, Rod Mauler, who both ran to the library after hearing the gunfire.
"We are confident that the murderer knew they were in his immediate area," Robinson said.
"James Englert is a hero, he saved lives," Robinson said.
"I am confident and believe strongly that the reason this incident took less than 1 minute and 20 seconds was the result of a very effective lockdown protocol that went into place immediately in collaboration with immediate and timely response by an armed school resource officer and an unarmed school security guard."
Robinson said Claire Davis' family asked Englert to serve as a pall bearer at her funeral last Saturday. He did.
The sheriff also mentioned that a quickly implemented lockdown protocol helped save lives.
He said after the first gunshots were fired, the janitor started the lockdown procedures.
-- Investigation continues
While the investigation into the shooting continues, Arapahoe County Undersheriff David Walcher said the Sheriff's Office plans to hire a third party to conduct an investigation into the Sheriff Office's actions and the lessons learned.
Arapahoe County District Attorney George Brauchler said he wants the investigation to be transparent, but that it's too early to unseal court documents. Brauchler said nearly a dozen search warrants have been executed and that others will be.
"The goal here is to come up with as many answers as possible," Brauchler said. "And look, the bottom line for us is, it's not just about fact finding, it's about whether there is any justice that can be obtained in this process."