LITTLETON, Colo. -

The principal of Columbine High School, who helped shepherd students to safety during the 1999 shootings there, is retiring after 18 years of leading the school.

In a letter to parents Tuesday, Frank DeAngelis said he would step down at the end of the school year.

DeAngelis was in his office the morning of April 20, 1999, when two student gunmen launched an attack on the school, killing 13 people.

He shepherded a group of about 20 students to safety that day, and he survived with no physical injuries. However, he says the shootings left him with severe anxiety attacks that felt like heart attacks and contributed to the end of his marriage.

DeAngelis tells KMGH-TV that he's healthier now and believes schools everywhere are safer because people are now more likely to report suspicious behavior.