Ten died at the scene, two more at hospitals, and the thirteenth was lost in a miscarriage caused by the trauma.
Fifty-eight more people were injured, at least eight of which are still in critical condition.
This post shall serve as a memorial for the twelve that died in the tragedy.
Alex Sullivan, 27, was out celebrating his birthday with his friends. Sunday would've been his first wedding anniversary.
He was a graduate of Gateway High School, in Aurora.
His family remembers him for having a huge heart.
Her family "hope[s] this evil act doesn't shake people's faith in God."
She had been in the process of saving money for a trip to India, with coworkers.
Originally from San Antonio, Texas, she had moved to Denver for an internship towards her dream.
She was a huge Colorado Avalanche fan, and didn't miss a game.
In June she had just left a mall in Toronto when a gunman opened fire there. Her blog talked about the incident and how it affected her.
"I was shown how fragile life was on Saturday. I saw the terror on bystanders’ faces. I saw the victims of a senseless crime. I saw lives change. I was reminded that we don’t know when or where our time on Earth will end. When or where we will breathe our last breath."
He was stationed at Buckley Air Force Base as a cryptologist with the US Navy.
Samantha Younger was wounded in the leg, but survived the onslaught because of his sacrifice.
He moved to Aurora, in November 2011 from Butler Township in Ohio.
He was a graduate of Butler-Vandalia High School.
He was an Air Force cyber systems operator at Buckley Air Force Base.
When the shooting started he dove in front of a friend from the base, taking a bullet that would have hit her.
A very active person, he could always be found playing one sport or another.
His friends knew him as a huge nerd, who had named his black Scion "The Batmobile".
She had just begun learning to swim, and loved it.
He sacrificed himself to save Jansen Young's life.
Blunk was a former member of the US Navy, and had been planning on reenlisting, in hopes of becoming a SEAL.
He had been scheduled to spend the week in Reno, Nevada to visit his children who are two and four.
He was set to attend Rocky Mountain College of Art and Design in the fall.
AJ's friends and family remember him as someone who would do anything for a laugh.
Alex shielded his girlfriend, Amanda Lindgren, from bullets, saving her life.
He had recently earned his master's degree in counseling psychology from the University of Denver.
Wingo had formerly worked for the US Air Force as a translator and had recently started a new job, in the medical field.
Her family remembers her as an extremely giving person.
He had taken his two teenage kids to the movie.
Both his kids escaped unharmed.