A child therapist said Sunday scars from Friday's school shooting could linger for a lifetime for some students and staff.

Karl Pierson, 18, walked into Araphoe High School Friday with a shotgun, a machete and a large amount of ammunition. Police said he shot and critically injured 17-year-old Claire Davis. Pierson was found dead inside the school minutes after the shooting was reported. Investigators say he took his own life.

Davis remained in critical condition Sunday afternoon.

The assault at the high school lasted 80 seconds, but child therapist Erica Laue said the memories could last a life time.

"Surviving a traumatic incident like this can leave a whole lot of scars," said Laue.

She said post traumatic stress disorder will be a common diagnosis for students and teachers that were at the school that day.

"It can also involve symptoms that don't look like post traumatic stress disorder," said Laue. "Things that look more like bipolar disorder or depression, a generalized anxiety."

"A lot of people feel like, 'There is something wrong with me because I can't function the way I used to,'" said Laue. "You're not going to for a little while."

She said counseling and support groups will help, but it takes time.

"Even in five years, 10 years, 50 years, they look back and they say, 'I no longer feel a huge emotion connection to this event,' but they will still remember it.  Something like this wears a groove in your brain and you never walk away from that," said Laue.