DENVER (AP) — Authorities were investigating a 14-year-old girl's actions before they say she attacked two students with a hammer at Columbine High School in the first assault with a weapon since the deadly shootings there in 1999.

Investigators Monday were trying to gather additional details, including where the girl got the hammer, said John McDonald, Jefferson County School District's executive director of security and emergency management. The Jefferson County sheriff's office — the same agency that investigated the shootings nearly 13 years ago — is also working to determine whom the girl spoke with before the attack.

It was unclear what sparked the attack Monday morning at the school outside of Littleton, about 13 miles (21 kilometers) southwest of downtown Denver.

The 14-year-old targeted a 15-year-old girl in a hallway leading to bathrooms, Jefferson County sheriff's spokeswoman Jacki Kelley said.

Aaron Flowers, 16, told Denver television stations that the 15-year-old was struck in the hand. He said he also was hit in the hand and ribs while trying to grab the hammer from the attacker, after another friend pushed the attacker down.

The victims were expected to recover fully from their injuries, sheriff's officials said. They were taken to a hospital and later released.

Flowers said the girls had had problems before. He didn't immediately return a message from The Associated Press seeking comment.

Kelley declined to release additional information, saying the attack remained under investigation.

The Littleton high school was the scene of one of the worst school attacks in U.S. history when students Eric Harris and Dylan Klebold opened fire on April 20, 1999. They killed 12 classmates and a teacher and wounded 26 others before killing themselves in the school's library.

The attack had a deep impact on the nation's law enforcement community, which developed new tactics for dealing with "active shooters." Schools developed ways to prevent bullying and added measures for school safety that included adding metal detectors, fences, ID badges, dress codes, security patrols and surveillance cameras.

Since the 1999 shootings, unarmed students and teachers have taken active roles in confronting attackers at schools when possible.

In February 2010, a math teacher on sidewalk patrol at a middle school tackled a gunman who opened fire with a bolt-action rifle, wounding two students. Other teachers joined in to restrain the gunman at Deer Creek Middle School, which is less than two miles from Columbine.

McDonald said students at Columbine grew up with the knowledge of the 1999 shootings but there's no indication that the latest attack is related.

"It's our history, not our legacy," he said.