Authorities also said it was not yet known who it was, and McGraw declined to say.
Parents gathered on the campus of 2,500 students expressed dismay and took adequate steps for the safety of their children.
Denver school officials said after the shooting that they would put armed officers back in the city's public high schools amid vacillating security talks.
None of the schools were on resource at the time of Wednesday's shooting. Denver Police Chief Ron Thomas said.
Authorities said there was a shooting in the office area just before 10 a.m. as Lyle was being searched under some form of "security."
Thomas has also stated to the best of his knowledge that the gun that was used at the time of the firing has not yet been recovered.
Hundreds of East High School students skipped class on March 3 following the death of 16-year-old Luis Garcia.
Denver Public Schools Superintendent Alex Marrero said two armed officers will be placed at East High School by the end of the school year.