For Marrocolo and others, the anniversary of 9/11 is a time to remember and to remind others of the horror of that day.
"What concerns me is that I think people are starting to forget how horrible 9/11 was," Marrocolo said, ". . . and if I can't remember these precise details, I feel like my ability to explain the event becomes more difficult."
And so, she and others turn back the clock to 8:46.40 a.m. on Sept. 11, 2001.
MaryAnn Marrocolo, former emergency planner for New York City, who worked on the 23d floor of Seven World Trade Center.
"I was going through the Brooklyn-Battery Tunnel, and I had just come out of the tunnel on the Manhattan side when someone from my office called me and said a plane had just hit the World Trade Center. . . . At first I didn't believe him.
"I wasn't going to be able to get through all the traffic, so I walked from the tunnel to the trade center . . . and I ran through the plaza area to Seven World Trade Center.
"A lot of smoke and debris was falling from above. A couple of times, I looked up, and you could clearly see people standing at the edges of where the windows were broken, or they were actually falling through the sky. I saw maybe five or six people who were in the process of falling."
Marrocolo was inside the city's Emergency Operations Center (EOC) on the 23d floor when the second plane hit.
"There weren't any windows. We saw it on TV and you felt the building shake. . . . That's when we realized that this wasn't just a freak accident, that this was some orchestrated attack.
"We went down the stairs - 23 flights - and then we ended up in the lobby of Seven World Trade Center. . . . Outside, there was glass falling and things hitting the ground."
Marrocolo was helping to set up a triage area in the lobby and telling city personnel who were arriving on the scene where the emergency operations center had moved when the South Tower collapsed.
"The glass in the lobby was breaking, and it was clear something bad was going to happen. . . . We were trapped very briefly, and we couldn't figure how to get out of the building, because a lot of the entrances were blocked and the lobby had been completely destroyed.
"When the dust cleared a little bit, it was amazingly quiet . . . and then the sound most disturbing was, you could hear the firefighters' pass devices, the accountability devices. When a firefighter doesn't move for a period of 30 to 60 seconds, this device goes off. It's a loud beeping noise, and I remember you could hear a lot of that. It was very eerie, because that means they're not moving."
Lt. John O'Neill, Philadelphia firefighter and member of a federal urban search and rescue task force, which was first on the scene.
"I had just come off night work. . . . I came home, got something to eat. My wife was at work, the kids at school. I was home by myself.
"Once the building came down, I knew we were going.
"I got all my gear together, had it by the front door, waiting for the call to mobilize.
"The most vivid memory I have today - even more than Ground Zero - is when my daughter walked into the house and saw my gear, she said, 'You're not going, are you, Dad? Why are you going?' My explanation to her was, That's what I'm trained to do, that's what people do when people need help.
"We left here at dusk, at 8 o'clock. I remember vividly, the sun was going down. It was a very beautiful day, sunny and clear.
"Everyone was anxious. They wanted to get there, they wanted to do something.
"We traveled in a convoy. There were 80 personnel, two buses, two tractor-trailers, two box trucks, pickup trucks and Suburbans.
"There was a lot of paranoia. . . . We were getting ready to go through the Holland Tunnel, and they stopped us. We had to divert out of there because they were worried about a white van that had explosives, which was not too far in front of us, only five cars ahead of us.
". . . Everyone backed up. We were in a convoy, and convoys don't ordinarily back up. We ended up in the Meadowlands and turned around."
O'Neill arrived on the night of Sept. 11. His crew bunked at the Javitz Center and arrived at Ground Zero the next morning. They set up operations in a gym at the American Express Building.
"There was a lot of stuff missing. There was no concrete, no big blocks of concrete. It had all been pulverized. If I can remember the site for anything, it was the dust, all the white dust. It looked like snow.
"You had fire trucks torn in half. You had people all over. . . . There were fire trucks burning, police cars that were burning, ambulances that were burning, all these crushed vehicles.
"The canines on our team are live search dogs. They're looking for lives, not cadavers. . . . One of the dogs, Reilly, had hit on something and gave his sign to his handler, and Chris turned to us, and he said, 'Look, the dog's getting a hit here.'
"There were numerous volunteers, trying to help out. They hopped on the dog before we could size up the situation, and they started right on it. They started shoveling and moving, and moving debris away, and they brought the dog in again. And the dog didn't get a hit again. The dog had gotten a hit on a small piece of a person that might have been there."
Elsie Goss-Caldwell, a West Philadelphia tax preparer, whose son, Kenneth Caldwell, was killed in the collapse of the North Tower.
". . . I was just sitting there on the edge of the bed, getting ready to come into the office.
"Then the phone rang, and it was Kenny. He said, 'Mom, I just want to let you know, I love you.' I was thinking, he's so silly, because the night before we were on the phone just laughing and talking. He had had a busy week the week before because he had to take clients out to dinner and the theater, and I was teasing him, saying I wish I could be that busy.
"All of a sudden, he said, 'I have to get out of here because there's a bomb.' And he was gone. I never spoke to him again . . . never, never, ever.
"That was it. I don't know if he hung up or got disconnected. All I know is, he was gone.
"I turned to [daughter] Keisha and said, 'We've got to go! We've got to find Kenny!'
"Then Natalie, Kenny's girlfriend, she called, and she was like, 'Mom, did you get a message from Kenny?'
"For some reason, when Kenny called her, it went directly to voice mail. And when I heard her message, he was so frantic, so scared, like he was running, and it was in his voice, like he was trying to get away.
Elsie's son Leon arrived the next day from graduate school in Nebraska. A caravan of seven cars headed to Manhattan.
"We sent some to New Jersey, and we made Kenny's apartment our central meeting place.
"We went to the armory, and there were lists of names. . . . I remember when we came outside, there were all these people standing across the street. They were just standing there. I thought, 'What are they doing?' And when we walked across the street, there were all these fliers for all these missing people . . . just thousands."
"At nighttime, I'd call his cell phone, and I would tell him I was coming to get him, and I'd tell him I loved him and not to be scared and that Mommy was coming.
". . . It would ring and go to voice mail, and his voice would come on, and I'd leave a message."
Contact staff writer Jennifer Lin at 215-854-5659 or firstname.lastname@example.org.