The disgruntled professor who shot four educators at the University of Nevada, Las Vegas - killing three - had apparently taken a powerful erectile dysfunction drug before going on his rampage.

Anthony Polito, 67, opened fire on the fourth floor of the Lee Business School at 11.45am on December 6, killing Professors Patricia Navarro Valez, 39; Cha Jan ‘Jerry’ Chang, 64; and Naomo Takemoru, 69, and critically injuring a fourth.

He then died in a shootout with police who rushed to the scene.

An ensuing autopsy report has since revealed that Polito had tadalafil - the scientific name for Cialis - in his bloodstream, the Las Vegas Review-Journal reports.

Polito’s bloodstream tested positive for 84 nanograms per milliliter of the erectile dysfunction drug - which can last up to 36 hours in the body, according to the autopsy report on June 15.

He also tested positive for oxycodone, with 15 nanograms per milliliter in his bloodstream - far below the US Department of Transportation testing threshold of 100 nanograms per milliliter for urine tests.

Neither Cialis nor oxycodone are known to increase risk-taking behavior the way alcohol does, Matthew Johnson, a Johns Hopkins University specialist who studies psychological effects of drugs, told the Review-Journal.

He also noted that it is unclear whether Polito took the oxycodone shortly before his death, or if he had taken a large amount in the past.

It is believed Polito opened fire on the Las Vegas campus after feeling jilted that he was rejected from a teaching position at the school.

He had been obsessed with Sin City, his former students have said, and had applied to several jobs at various colleges and universities across Nevada - but was denied the job each time.

On the day of the attack, police said Polito went to several floors of the business school before he was killed in a shootout with two university officers outside the building.