Omar Mateen, the man responsible for the worst mass shooting in US history, pledged allegiance to Islamic State to police during the attack.
Mateen killed 49 people at a gay nightclub in Orlando in June, before being shot dead by SWAT teams after a three hour stand-off.
Recordings of phone calls between the man and the police reveal that he grew increasingly angry with them as they tried to keep him on the phone.
Although transcripts of what the attacker told police have previously been released, this is the first time the audio recorded during the attack has been heard by the public.
The audio reveals that police were not certain of Mateen's whereabouts at the start of the call. As the gunman hung up several times, officers formulated a strategy to deal to him.
In one call he states calmly: "You're speaking with a person who pledged his allegiance to the Islamic State of Abu Bakr al Baghdadi and Allah."
Mateen also hit out at US involvement in Iraq and Syria, saying, "They're killing a lot of innocent people, so what am I to do here when my people are getting killed over there? You get what I'm saying?"
He also praised his "homeboy", Boston marathon bomber Tamerlan Tsarnaev.
Despite officers' attempts, the phone calls did not gain the police any information, and their attempts to make Mateen release hostages also proved unsuccessful.