This story has been updated.

Like on any other day, 23-year-old Feidin Santana, a Dominican immigrant to South Carolina, was walking to work on Saturday afternoon, talking on his cellphone. As he glanced over a chain-link fence that separated him from a scrubby patch of ground at the side of the road, something caught his attention. What he saw and heard — and what he did about it despite a deep-seated fear of the consequences — would soon shock the conscience of North Charleston and the nation.

And it would change him, perhaps forever. “My life … changed in a matter of seconds,” he said on MSNBC’s “Morning Joe” on Thursday.

Santana shot the video on Saturday that shows a white police officer firing his pistol at a fleeing, unarmed black man, Walter Scott. So powerful and troubling were the frames captured by Santana that North Charleston Police Chief Eddie Driggers would later describe himself as “sickened” by what he had seen. The officer, Michael Slager, 33, was charged with murder.

Santana laid low, frightened for days, both before and again after he handed the video over to the Scott family. Then on Wednesday, he spoke out in interviews with MSNBC’s Chris Hayes, “NBC Nightly News” host Lester Holt and, on Thursday, with MSNBC’s “Morning Joe.”  He described the ordeal he had been through.

What he saw was a struggle between a black man and the white police officer. “I saw Mr. Scott running on the same street I’m heading to my job,” he said on “Morning Joe.” “Then I saw the officer chasing him. I just decided to chase them to see what was happening.”

What he heard was the sickening electric sound of a clicking Taser. That’s when Santana ended the phone call, he told reporters, and started filming, running to keep up with the action. “I was hearing the Taser sound,” he said, “and the yelling of Mr. Scott, and that’s when I decided to do the recording.”

He told NBC News that at first the two men were on the ground.

“I remember the police [officer] had control of the situation,” he said. “He had control of Scott. And Scott was trying just to get away from the Taser. But like I said, he never used the Taser against the cop.”

“As you can see in the video, the police officer just shot him in the back,” he added. “I knew right away, I had something on my hands.”

Still, Santana said he was afraid of what he had — video footage that contradicted what police had reported. He was afraid of what might happen to him if he handed it over to police. He did go to the police station but only briefly, he told interviewers. He was asked to wait when he arrived, but decided to leave.

“I felt that my life, with this information, might be in danger,” he told MSNBC. “I thought about erasing the video and just getting out of the community, you know, Charleston, and living someplace else.” On “Morning Joe,” he added that his family was “afraid of what would happen” to him.

[How a cellphone video led to murder charges against a cop in North Charleston]

But he heard how police were describing the killing — that Scott had grabbed the Taser, so the cop opened fire — and that bothered Santana. “I knew the cop didn’t do the right thing,” he said.

On Sunday afternoon, Santana returned to the scene. He said he thought about the victim’s family and knew they would want to know the truth. He finally decided to make contact with them. “I felt a need to look for justice,” he said.

Santana went to a vigil for Scott, according to victim’s brother, Anthony Scott, and told him, “I have something to share with you,” the Los Angeles Times reported. He began to play the video.

When the family saw it, Santana told NBC News, “they were very emotional.”

On Tuesday night, the video was released to Charleston’s Post and Courier and the New York Times — and played for the world.

The footage showing Saturday’s shooting is key because it presents evidence that directly contradicts Slager’s account, which ultimately led to the officer’s murder charge. Since it was released, many have praised Santana for stepping onto a very public stage, including Scott’s family attorneys.

[In North Charleston, urgent promises of change to avoid another Ferguson]

People on social media are calling Santana a hero. A Facebook page called “Fans of Feidin Santana” popped up late Wednesday, referring to him an “American hero,” a “patriot” and an “angel on earth.” Fans were talking about setting a GoFundMe page to raise donations for a reward.

“I’m proud of you because you have the courage to do the right thing so this criminal can pay for his crime,” one commenter wrote. “…We need more people like you on this earth so we can stop the abuse and the killing of our Black and Latino brothers by law enforcement. God bless you.”

In the wee hours of Thursday morning, Santana posted a reply on the page.

“Hey guys … as you can see my English is not my first language,” he wrote. “But I’m very thankful of everyone support. Even though this is very new to me and my family but never imagined that this will turn with so much love (which make it a little bit easy for me). Thank you for everything! For all those kind words … thank you.

“We all equal, we all human, let’s love each other and stop all this killings in our world.”

Asked how he summoned up the courage to shoot the footage in full view of police, he said on “Morning Joe:” “I don’t know what happened to me at that moment to be honest. I’m a great believer in God. Maybe he put me there for some reason.”

Maybe, he said, that let him put his fear aside. “Maybe I tried to act like a reporter or something,” he said.

But, he said, it’s not something he can feel happy about.

The officer “has his family, Mr. Scott also has his family,” he told NBC News. “But I think, you know, he [the officer] made a bad decision, and you pay for your decisions in this life.”