Washington (CNN) Amid outrage over the acquittal of the officer who shot and killed Philando Castile, many activists and some gun owners seem to agree on one thing: The National Rifle Association should not remain silent.

In a Wednesday letter addressed to NRA CEO Wayne LaPierre, activist Tamika Mallory -- one of the founders of the progressive Women's March -- slammed the NRA for demonstrating "a complete disregard for the lives of black and brown people in America" for failing to "make any statement defending the civil rights of Mr. Castile."

The letter also slammed an April anti-protester, pro-police NRA ad featuring conservative commentator Dana Loesch, which Mallory characterized as a "vicious and incendiary video calling for armed conflict."

An NRA spokeswoman confirmed to CNN that the NRA has received the letter, but a request for comment was not returned.

Jeronimo Yanez, the Minnesota police officer who fatally shot Castile -- a 32-year-old Minnesota man who was a licensed gun owner -- during a traffic stop last year, was found not guilty of second-degree manslaughter on June 16. He also was acquitted of two counts of intentional discharge of firearm that endangers safety.

An audio recording captured Castile telling Yanez he had a gun in the car, and the officer telling Castile not to reach for it. Seconds later, Yanez opened fire.

"As an @NRA member, I agree that the NRA should speak out on the Philandro Castile shooting. This is a travesty," an editor of the conservative blog HotAir tweeted.

As an @NRA member, I agree that the NRA should speak out on the Philandro Castile shooting. This is a travesty. — Jazz Shaw (@JazzShaw) June 20, 2017

After coming under criticism for their silence immediately following the incident, the NRA issued a statement last July without naming Castile, calling the incident "troubling" and vowing that "the NRA will have more to say once all the facts are known."

But the group has said nothing since.

Colion Noir, a staunch NRA defender who hosts a show on NRATV , lamented the not-guilty verdict in a passionate online post , saying "Philando Castile should be alive today," but he also dismissed NRA critics, who slammed the gun rights groups' silence on Castile.

Philando Castile Should Be Alive Today



Read: https://t.co/Hmi6DCJAA4 — Colion Noir (@MrColionNoir) June 18, 2017

The Media went after the @NRA for not saying something after Sandy hook. Does that mean they don't care about little white kids? Come on ppl — Colion Noir (@MrColionNoir) June 20, 2017

"The Media went after the @NRA for not saying something after Sandy hook. Does that mean they don't care about little white kids? Come on ppl," he tweeted.

And in response to a tweet by CNN commentator Bakari Sellers, saying, "NRA, rabid 2nd Amendment folk, hella quiet. #PhilandoCastile did everything right," Noir tweeted: ""Bro Chill, have been speaking on it, did a video on it when it happened and twitted about it. Stop w/ the ambiguous race baiting."

Bro Chill, have been speaking on it, did a video on it when it happened and twitted about it. Stop w/ the ambiguous race baiting. 🙄 https://t.co/VuQjBcTJIG — Colion Noir (@MrColionNoir) June 16, 2017

Democratic Rep. Bonnie Watson Coleman, a member of the Congressional Black Caucus, criticized the NRA's silence in a speech on the House floor last week and tweeted, "If the @NRA isn't here to protect law abiding gun owners like #PhilandoCastile, then who are they here to protect?"

If the @NRA isn't here to protect law abiding gun owners like #PhilandoCastile, then who are they here to protect? pic.twitter.com/6fIdYi1YcC — Bonnie WatsonColeman (@RepBonnie) June 21, 2017

Asked about the NRA's silence on Castile, President of the National African American Gun Association Phillip Smith told CNN that while his organization is "not concerned about who said what," the shooting is "one of the clearer cut cases" that demonstrates racial bias against black men.

"There's an automatic assumption of guilt when you see an African-American male walking down the street with a gun on their hip," Smith said Thursday.

"Most folks that are buying the gun that are in our group are just buying a gun because they want to protect their family," he added. "There's always this fight you have to overcome -- that I'm a good guy just trying to exercise my Second Amendment rights like everyone else."

Yanez testified that he feared for his life because Castile put his hand on his firearm, not his wallet or identification papers, and was pulling the gun from his pocket.

Prosecutors portrayed Yanez as a nervous officer who was too quick to pull the trigger based on an unreasonable suspicion that he was a robbery suspect.

"I didn't want to shoot Mr. Castile," Yanez testified. "That wasn't my intention. I thought I was going to die."

"Let's go NRA. I know y'all are for the 2nd amendment. Are you also for equal protection?" John Legend tweeted, noting the NRA's silence following the shooting last year.

Let's go NRA. I know y'all are for the 2nd amendment. Are you also for equal protection? https://t.co/PaKMcZ7ina — John Legend (@johnlegend) July 7, 2016

.@NRA we know that NOONE fights so hard for "the right to legally bear arms" more than you do. That said... #PhilandoCastile? Anyone? — Questlove Gomez (@questlove) July 7, 2016

".@NRA we know that NOONE fights so hard for 'the right to legally bear arms' more than you do. That said... #PhilandoCastile? Anyone?" rapper Questlove tweeted, echoing Legend's point.