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The FBI will release a partial transcript Monday of Omar Mateen's phone calls with police negotiators during a mass shooting in Orlando last week that left 49 dead, Attorney General Loretta Lynch said Sunday.

Lynch said on NBC's "Meet the Press" that during the calls, a police negotiating team was trying to determine who Mateen was, "where he was and why he was doing this, all while the rescue operations were continuing."

Authorities have previously said that during three conversations with a 911 dispatcher, Mateen pledged allegiance to ISIS' leader, Abu Bakr al-Baghdadi.

Mateen allegedly also said he admired the brothers who bombed the 2013 Boston Marathon, describing them as his "homeboys," as well as Moner Mohammad Abu-Salha, a 22-year-old Palestinian-American from the same town as Mateen who carried out a suicide attack in Syria.

Abu-Salha carried out the bombing on behalf of Al-Nusra Front, a terrorist rival of ISIS.

When asked what was being left out of the transcript, Lynch said would not help to "further proclaim this individual's pledges of allegiance to terrorist groups and further his propaganda."

The news came ahead of a planned Sunday vigil in Orlando, which was expected to draw as many as 20,000 people.