Officer JD Smith was 10 miles away when he heard the voice on the radio: "Shots fired, officer down."
"That’s the worst thing I’ve ever heard on the radio. Immediately, a pit in your stomach, stomach is in knots, you don’t know what’s happening," Smith said. "You're thinking, 'I got to get there. I got to get there.' I don’t know how fast I was going, but it wasn’t fast enough."
The 25-year old officer raced downtown, headed toward El Centro College. When he got downtown and parked his cruiser near the Crowne Plaza hotel, he remembers chaos, confusion and gunfire.
"We still were getting reports that there’s three or four shooters, so we don’t know what’s going on. Your head is on a swivel," he said.
"Someone comes over the radio that there’s suspects at the Omni," he continued. "So we sprint down to the Omni, but there wasn't anyone there. So we raced back."
That's when Smith noticed a man standing alone in the street, possibly in the line of gunfire. Smith said he told him, "Get behind me, and stay small."
For more than an hour, he wouldn't let the stranger out of his sight -- until it was safe to escort him across the police perimeter.
"He was there. I have body armor on. He doesn’t. Is there any question what I should do? I just put myself in front of him. At that point, it’s my job to take a bullet," Smith said, calmly.
"That’s why I became a police officer. If it came to that -- then that’s what it would come to," he added. "Any officer would rather give their life than have a citizen give theirs."
The stranger crouching behind Smith was former Dallas Voice photographer Robert Moore.
In the heat of the crisis, he snapped a few photos, explaining in a public Facebook post: "I was photographing the march and crossing the intersection when the firing started. I ran for cover behind the closest car and became trapped."
Moore added, "I don't know his name, but I won't forget him."
The Facebook post has been shared nearly 8,000 times, and other police departments are asking for prints.
Smith said he's been recognized a few times over the last week as the officer in the photo. He he has mixed feelings about it.
"I’m grateful, the photo is awesome. I don’t look that good in real life," he joked.
"But I just think more of the focus needs to be on those five officers who gave their lives that night, and the eight that are injured," he said. "Honestly, I’m just a dude who got his picture taken. Just doing my job."
Over the last few days, Smith mourned at two police funerals, DART Officer Brent Thompson and his friend Sgt. Michael Smith.
"I haven’t had much time to process. You have little moments to grieve, and it’ll take time," he said. "We lost four officers and a DART officer. That’s five. It sucks. There’s just no other way of putting it."
Smith is now back on patrol -- working nights in North Dallas. He said there's a heaviness now when he's out on patrol; a somber mood that'll take time to heal.
"You think about it. Honestly. You have little moments where you grieve, then you get back. Then you still have a job to do," he said.
Smith has been with Dallas police for three years. His cousin is a fellow officer. His uncle and grandfather also served with Dallas police.
"I don’t like taking time off, because I love my job. I love patrol. It’s the most direct form of policing, we have the most contact with people. We get to help people."
Smith said he hopes that's the enduring message of the viral photograph: that police are here to help and they're here to protect.