But when her Facebook Live video was played during the officer's trial Tuesday, she couldn't bear to watch. She turned her head away and wept.
There was nothing Reynolds could do to save her boyfriend, Philando Castile. As he bled, the officer kept his gun pointed into Castile's car.
Reynolds took the stand for a second day to testify in the manslaughter trial of police officer Jeronimo Yanez.
Prosecutors asked Reynolds why she broadcast Castile's final moments online. The video quickly went viral, sparking nationwide "Black Lives Matter" protests and renewing the debate over excessive use of force against black men.
Reynolds also said she wanted everyone -- including her young daughter -- to know the truth.
"People are not protected against the police," she replied.
The first day of Yanez's trial presented two very different narratives.
Defense lawyer Paul Engh said Castile's fate was a result of his inability to follow orders, possibly because he was high on marijuana and had THC in his system.
Castile, 32, ignored the St. Anthony police officer's commands and reached for his weapon when he was instructed not to do so, Engh said.
Yanez was trained on reasonable use of force and had never been disciplined during his time with the police department, the defense lawyer added.
But prosecutors argued Yanez was negligent by not giving Castile clear direction when he learned Castile had a weapon.
"He didn't tell him to freeze" or put his hands up, Assistant Ramsey County Attorney Richard Dusterhoft said. "Officer Yanez's actions led to Philando Castile's death."
Yanez is charged with second-degree manslaughter, plus two felony counts of dangerous discharge of a firearm for allegedly endangering Reynolds and her daughter. Reynolds' then-4-year-old child was sitting in the back seat when Castile was shot in the driver's seat.
One of the bullets Yanez fired pierced the front seat and came very close to the girl, prosecutors said, adding that another bullet could have hit Reynolds but was blocked by the front seat armrest.
Reynolds: My boyfriend supported police
When Reynolds took the stand Monday, she wept as soon as she saw a photo of Castile.
Castile, a school cafeteria worker, had no animosity toward police, she said. During her half-hour testimony, Reynolds said she and Castile had sometimes attended police barbeques to "show support."
Though Castile was not her daughter's father, Reynolds said he cared for the child and helped provide for her.
It was Castile's protective nature that made him want to get a gun permit, Reynolds said. Recent killings in the neighborhood, along with drugs and prostitution, spurred Castile to carry a gun for self-defense, she said.
"He always had it for protection for himself and protection for his family," she said.
When Yanez pulled Castile over on July 6, allegedly for a broken taillight, Castile mentioned to the officer that he had a weapon on him.
Minutes later, he was dead.
The fatal encounter
Reynolds' Facebook Live broadcast did not show what led up to the shooting, nor the shooting itself. But it did show Reynolds crying and screaming in bewilderment as to why her boyfriend was shot.
"Please don't tell me he's gone!" she screams. "Please, Jesus, no!"
Castile's last words were, "I wasn't reaching for it," insisting he wasn't trying to get his registered handgun, according to a transcript in the criminal complaint
Castile had a permit to carry a firearm in his wallet. He had been reaching for his ID in his back pocket when he was shot, Reynolds said.
To fill in the gaps, prosecutors called former St. Anthony Officer Joseph Kauser. He was second on the scene after Yanez called over the radio for backup.
In an audio recording played in court, Yanez said he was stopping a car with two occupants to check their identifications because one of them looked like a robbery suspect based on his "wide-set nose."
Kauser approached Castile's car on the passenger side and noticed Reynolds and her daughter. It felt like a typical traffic stop and everything seemed "relaxed and calm" from his vantage point, Kauser testified.
"I didn't feel threatened at that point from where I was standing."
In fact, he said he was surprised when the gunshots went off. At no time during the stop did he see anyone in the vehicle with a gun and he was unaware that Yanez had pulled his weapon. He did not see him fire the gun, he testified.
Dashboard camera footage from Yanez's vehicle showed him pulling out his gun. Seconds later, Yanez fired seven shots, five of them striking Castile.
The dashcam audio captured Yanez off camera relaying the events to a supervising officer. He said he told Castile not to reach for the gun and that Castile's "grip (was) a lot wider than a wallet." Kauser said he did not hear the conversation between Castile and Yanez because he was focused on Reynolds.
Yanez told the supervising officer he did not know where the gun was and that Castile did not tell him where it was.
When asked if Yanez followed protocol during the incident, Kauser said, "I think he did what he was supposed to do in that situation."
Editor's note: A previous version of this story incorrectly described the relationship between Diamond Reynolds and Philando Castile. Reynolds was his girlfriend.