The U.S. Border Patrol released a timeline of the deadly shooting at the U.S. Border Patrol Rio Grande Valley Sector Annex in McAllen.

The gunman, identified as 27-year-old Ryan Louis Mosqueda of Michigan, was killed after firing toward the federal building and the agents inside; three people were also injured in the incident.

According to a news release, Mosqueda arrived at the annex building, in a sedan on July 7 at around 5:30 a.m. He remained in his vehicle for approximately 15 minutes before exiting and standing in the parking lot "wearing a mask, a vest resembling a body armor plate carrier, shorts and carrying a black bag."

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At around 5:50 a.m., a law enforcement information system specialist assigned to the annex arrived in his personally owned vehicle. The specialist noticed Mosqueda standing between two other vehicles in the parking lot, according to the news release.

The news release said as the specialist parked his vehicle, Mosqueda raised an AR-15 style rifle and began firing. The specialist retrieved his personally owned pistol and fired approximately three bullets through the windshield. After firing, the specialist's pistol malfunctioned, and he called 911 to report an active shooter.

According to the news release, at around 5:54 a.m., Mosqueda approached the front doors of the building and fired his rifle several times at the entry doors, attempting to enter the annex. He then drew a pistol and fired several more times. Mosqueda attempted to open the doors, but ultimately failed to gain entry to the facility.

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As the McAllen Police Department arrived on scene, Mosqueda moved to a pedestrian gate on the south side of the annex and reloaded his rifle. Three Border Patrol agents at the facility heard the exchange of gunfire and responded to assist, according to the news release.

The news release said at around 5:55 a.m., the three agents were wearing marked U.S. Border Patrol body armor and identified themselves as law enforcement officers. They ordered Mosqueda to drop his rifle, but he responded by firing several bullets.

At around 5:56 a.m., the agents returned fire and struck Mosqueda, the news release said. Mosqueda sustained bullet fragmentation injuries on his left thigh and a bullet wound that pierced his left cheek and through his skull; he then collapsed.

According to the news release, the agents approached Mosqueda and found him unresponsive. They immediately secured his pistol and rifle. At approximately 5:58 a.m., agents requested emergency medical services.

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At around 6:10 a.m., EMS arrived on the scene, medically assessed Mosqueda but found no signs of life. A local justice of the peace pronounced him dead at the time of the shooting.

A police officer who arrived on scene at 5:54 a.m. reported that he sustained a wound from shrapnel to the leg and was transported to the McAllen Medical Hospital for surgery, according to the news release. Another agent was transported for ringing in his ears, and the specialist sustained glass shards in his skin.

On July 8, a Hidalgo County forensic pathologist conducted an autopsy of Mosqueda's body. The cause of death was determined to be a gunshot wound to the head, and manner of death was ruled a homicide.

The FBI is investigating the shooting.