The shooter 'methodically and deliberately' fired at students. A timeline of a school shooting tragedy

Authorities say at least 30 shots were fired, killing four students and wounding six other teenagers along with one teacher before the alleged shooter -- a student at Oxford High school -- was detained by police with rounds still in his handgun.

Zander Cumbey had walked into his afternoon high school classroom when he heard screaming outside in the hallway.

The cries were punctuated by a gunshot, he said.

"My teacher, he walked into the classroom; he locked the door, and he told us to call 911. And then we heard the rest of the gunshots go off, more screams," Cumbey told CNN.

Authorities say at least 30 shots were fired, killing four students and wounding six other teenagers along with one teacher before the alleged shooter -- a student at Oxford High school -- was detained by police with rounds still in his handgun.