US nightclub shooting autopsies released

More than a third of the 49 patrons killed during the Florida nightclub massacre were shot in the head, and most of the victims had multiple bullet wounds, according to autopsy reports released this week.

Only two victims had traces of gunpowder meaning most of the victims were likely more than one metre away when they were shot in the deadliest mass shooting in modern US history.

The autopsies show that about half of the victims had five wounds or more, and one victim had 13 wounds.

Gunman Omar Mateen was killed during a shootout with law enforcement officers following a three-hour standoff June 12.

"It shows he shot a lot and had a lot of ammo," said Dr Stephen Cina, a Colorado-based forensic pathologist, who has no connection to the case.

The large number of head injuries and multiple wounds on victims suggests Mateen was targeting his victims rather than shooting randomly, said Josh Wright, a former Florida Department of Law Enforcement firearms analyst who now has a forensics consulting firm in Tallahassee, who also has no connection to the case.

The Florida Department of Law Enforcement is investigating whether anyone died from friendly fire during the shootout at the gay nightclub. Officers knocked down a wall and stormed the club, killing Mateen in hail of gunfire. Mateen, who had pledged allegiance to the Islamic State, was shot eight times by police.