NEW YORK - It's a Day many of us will never forget, but one reporter brought our story to the national level, Scott Pelley.

I sat down with him on the CBS Evening News set in New York to hear how he remembers -- 20 years later.

"It came to me as a phone call," Pelley recalls. "I was actually driving to work that day."

That day was April 19, 1995. Pelley was just a correspondent working out of the network's Dallas bureau when his bureau chief called him.

"He said there's been some kind of an explosion in Oklahoma City, it's probably a natural gas explosion, whatever it is, it's a big deal, we want you to go straight to the airport," Pelley said.

Pelley said he had never seen or heard of the Alfred P. Murrah building until then.

"I remember walking up the street, turning the corner, seeing the building, it was at that point in my career the worst thing I'd ever seen," he remembers.

Kelly Ogle: "When did you know it was more than a gas explosion?"

Scott Pelley: "Well, when you saw the Murrah building just collapsed in the street that way, it didn't make sense that something like that could have cause that level of destruction."

And the level of coverage that followed, stories unfolding each day, and in the end, 168 of our fellow Oklahomans killed in the blast.

"The whole next couple of years was, for my career, all about Oklahoma City," said Pelley.

Soon after, authorities caught up with Timothy McVeigh, who detonated the rental truck full of explosives in front of the Murrah building.

Kelly Ogle: "When we got the final information that Timothy McVeigh had been arrested and that it was a domestic attack, we were floored."

Scott Pelley: "That was, though, an amazing bit of police work and police luck. Charlie Hanger, the police trooper stopping Tim McVeigh because his license plate had fallen off and then the FBI in Kansas putting together the vin number on the bomb truck with Tim McVeigh's name, just some of the most unbelievable police work that I've ever seen."

Mcveigh was executed for the bombing, and accomplice, Terry Nichols is currently serving a life sentence.

Kelly Ogle: "You heard more evidence then most of the public did, really, all of the public did, you think they got everyone?"

Scott Pelley: "Oh, I do. I actually do. Were there other people who might have known what was a foot? Maybe, but if too many people know about these things, they don't happen, because somebody talks."

Today -- the Oklahoma City National Memorial & Museum replaces the area where the Murrah building once stood.

Kelly Ogle: "The moment it happened changed the city but the way that the city responded to it changed Oklahoma City's view of itself."

Scott Pelley: "Not just the view of itself Kelly, but I would argue, change the world's view of Oklahoma City. The way those great rescue workers attacked that pile of debris, the way the city gathered around those people who had been injured and celebrated the rescue workers, and then rebuilt itself and created that triumph of a memorial. I think people all around the world looked at Oklahoma City and saw courage and saw compassion and a great deal to admire."