The Chicago Sun-Times reported Saturday that Steven Kazmierczak, a former NIU graduate student who opened fire in a campus auditorium on Feb. 14, had less than .025 micrograms of anti-anxiety drug Alprazolam, commonly known as Xanax, in his system, autopsy results released by the school said.

The newspaper reported toxicology tests also found trace amounts of nicotine and cold medicine, benzodiazepine and pseudoephedrine.

"This combination of drugs in his system could have had no effect whatsoever on his mental status," said Angelos Halaris, chairman of the Department of Psychiatry and Behavioral Neurosciences at Loyola University Medical Center.

Kazmierczak's girlfriend told CNN he had been taking Prozac, Ambien and Xanax, but had stopped taking the Prozac weeks before the shooting.

The newspaper said an autopsy found that Kazmierczak died of a "contact-range gunshot'' wound to his mouth, which caused skull fractures and a laceration of the brainstem.