Arapahoe High School students and supporters hold a candle light vigil during a one year remembrance ceremony on Clarity Commons, named for student Claire Davis, who was killed in a school shooting one year earlier, at Arapahoe High School, in Centennial, Colo., Saturday, Dec. 13, 2014.

(AP Photo/Brennan Linsley)

At Arapahoe High School on Saturday, people gathered to remember Claire Davis. She was shot and killed a year ago by a classmate who then killed himself.

As the community surrounding the school in Centennial continues to mourn Davis' death, some parents and alumni are calling for more transparency on the part of school administrators. They want to know more about the events leading up to the shooting and what security measures the school has put in place since. 

Brett Stewart is among them. At the time of the shooting, he was a senior at Arapahoe and wrote a commentary published in The Denver Post about his experiences. Later, he told "Colorado Matters" host Ryan Warner that he sought to provide a thoughtful account of events.

Now, Stewart has written a second commentary, from his vantage point as a former student now attending college in Chicago. He continues to pay close attention to news about the shooting, including the release in October of a report from the Arapahoe County Sheriff's Department.

That report revealed Karl Pierson, the shooter, planned the attack over a period of several months. The report included excerpts from Pierson's diary.
 
He writes that his "spine tingled with fear and pain" when he read the report.
 

Arapahoe High students and supporters holding a candle light vigil and watch as 14 white balloons symbolizing the Colo. students killed in school shootings since the 1999 Columbine school massacre are released, during a remembrance ceremony marking one year since the shooting at Arapahoe High School, in Centennial, Colo., Saturday, Dec. 13, 2014. 

(AP Photo/Brennan Linsley)

Last year, Stewart said he did not think the attack was premeditated. Now, he says he's haunted by the diary entries. 
 
"That's scary stuff. That's straight out of a horror movie," Stewart says.
 
Stewart says he is speaking out again because he wants to start a constructive conversation about what happened and whether the attack could have been prevented.
 
"He was clearly a distraught human who was in a very bad place," Stewart says.
 
He also notes Pierson was apparently on medications prescribed by a mental health professional, and had documented anger management issues.
 
"I want to have a conversation that needs to be had that is not being had," he says. "It's being pushed under the rug."
 
"There is a lack of transparency, or an apparent lack of transparency," he alleges of the school's administrators.
 

Colorado Gov. John Hickenlooper, center right, hugs Michael Davis during a remembrance ceremony marking one year since Davis' daughter, student Claire Davis, was killed in a school shooting at Arapahoe High School, in Centennial, Colo., Saturday, Dec. 13, 2014. 

(AP Photo/Brennan Linsley)

Neither Arapahoe High School or Littleton Public Schools responded to CPR's requests last week for an interview.
 
"The school and the district never responded to some very valid claims that were made... that potentially could have prevented this shooting," Stewart says.
 
Many of those claims have come from Cameron Rust and Christina Kolk, who were both security guards at Arapahoe High School on the day of the shooting. Each has said there were warning signs about the danger Pierson posed beyond those documented in the police report. For example, Rust has said that he once saw Pierson looking at pictures of guns on his computer in the school cafeteria.
 
Like Stewart, other alumni, some parents and even current students in the community are asking for school administrators to be more forthcoming with information. On a Facebook page for a group called "Parents at Arapahoe High School," several people have posted concerns about the administration.
 
Stewart says his search for answers is part of the healing process. "If we do not talk about this," he says, "that is counterproductive both to our schools and our society as a whole," because school shootings have become all too common.