The footage was released by authorities in Springfield, IL Monday -- which depicts Sangamon County Sheriff's Deputy Sean Grayson facing off with Massey earlier this month after she called the cops over suspicions of a prowler near her home.

In the video ... you see Grayson and his partner in Massey's house, where they're asking her to provide her ID -- and eventually, they tell her to get a boiling pot of water off the stove.

In response, she tells the officers she'll "rebuke [him] in the name of Jesus" -- which prompts a strong response from Grayson, who says ... "You better f***ing not, I swear to God I’ll f***ing shoot you right in your f***ing face," suggesting he perceived a threat from her.

Grayson draws his weapon and points it Massey -- which prompts her to duck on the ground ... at which point Grayson opens fire on her. Grayson's partner suggests grabbing a medical kit, but Grayson shuts that down -- noting there's nothing to be done since it's a head wound.

Upon realizing Massey is still breathing, Grayson relents and says he'll get his medical kit ... but the lifesaving efforts were unsuccessful.

Grayson defends his decision to shoot -- saying he didn't know what else to do ... not wanting to take hot water to the face. His assumption ... she was going to chuck the water. In the aftermath of this, Grayson was fired and is now facing charges of first-degree murder, aggravated battery with a firearm and official misconduct. He has pleaded not guilty.

There's been widespread outcry over this -- with many pointing to the racial dynamics at play -- and President Biden has even condemned the shooting, speaking out on behalf of Massey and her family ... who 46 says deserves justice.