Trent Brewer drove to a parking lot, planning to sell some weed. The transaction never happened.

Police in Springfield, Mo., found Brewer, 23, face-down in a pool of his own blood with no pulse on Dec. 12. He was declared dead at a nearby hospital.

Police say Darian Earl Hall, 18, pulled out a chrome semi-automatic handgun before the sale could happen, and opened fire on Brewer as he began to run away.

Hall has denied shooting Brewer, blaming another teen who was with him at the time. What exactly happened will eventually be settled in court.

Brewer's story follows a familiar pattern: drugs, an escalating confrontation and the presence of a gun leading to a death.

***

Beatriz Cintora-Silva took refuge at her sister's home immediately after telling police in Longmont, Colo., that her ex-boyfriend had kidnapped her, threatened her and threw her into a car dashboard. It was Saturday, Dec. 16.

The next day, police arrested Daniel Sanchez, 31, who spent Sunday night in jail.

Six hours after Sanchez left the Boulder County jail, a call came into 911:

"No, no, no, please, no," Cintora-Silva said on the call.

Gunfire rang out and the phone went silent.

Then, Sanchez picked up the phone.

"I just shot everyone right now," he said, according to a recording of the 911 call.

"You just shot everybody?" the dispatcher asked. Sanchez calmly replied "Yeah."

She asked for his name, but he didn't answer.

"I'm going to shoot myself right now," Sanchez said on the recording. The dispatcher pleaded with him.

It didn't matter. The line went dead.

Sanchez had shot and killed Cintora-Silva, her sister and her sister's husband before killing himself with one of the most deadly weapons in the United States.

It wasn't an AR-15, or an assault rifle -- it was a Glock .45-caliber handgun.

America's most deadly firearm