A view across Boylston Street from the grandstand at the Boston Marathon, snapped by John Walls of Arlington moments after the explosion as he was waiting for his wife and daughter to finish the race. (John Walls)

John Walls is a veteran of the Boston Marathon, having watched his wife, Cindy Walls, the girls’ track and cross country coach at Bishop O’Connell High School in Arlington, finish many of her 17 “Bostons” and having run the race himself. So shortly before 3 p.m. Monday, he knew that his wife and daughter Katie, a former champion runner at O’Connell, were not far away.

Walls was in the grandstand at the finish line with his sister-in-law and eight other family friends when the first explosion occurred across Boylston Street. “All of a sudden, a gigantic explosion and a ball of fire,” Walls said. “Then there was smoke, and the panic and chaos. And then the second one went off just a few seconds later. And I said, ‘Oh my God, we’ve got to get out of here. We’re going to die.’”

Cindy Walls said she and Katie were less than a mile from the finish. It was her daughter’s first Boston Marathon, and Cindy was telling Katie, ”We are a few minutes away from the greatest time you’re ever going to experience,” the final run through the cheering crowd. “And then a guy comes out and stops us and says, ‘There’s been an accident at the finish line.’ An accident, are you kidding me? And then someone comes out of the apartments and says two bombs went off. I knew my husband and sister were right there. My daughter and I were panicking.”

Suddenly the race was over. And in the uproar, Cindy and Katie Walls had no way to contact their family to see if they’d been hit by the blast.

Meanwhile, John Walls couldn’t believe what he was seeing as the smoke cleared. A former television news and sports anchor for almost 25 years, “I’ve seen crime scenes, but not anything like this,” Walls said.

“We saw all of the people on the other side of the street for a hour or so, cheering for runners and in just one split second, there was an explosion, and a blast, and smoke ... And they were gone. Sprawled all over the sidewalk. And you knew some were really, really hurt.”

Walls knew he had to guide his family and friends to safety. “But there’s panic, people are saying stay away from trash cans, stay away from buildings, get out to open areas,” he said. He shot a short video as they evacuated the area, and said he never lost cell phone service.

“I was getting all sorts of texts” from other family members, Walls said. But he knew his wife and daughter didn’t have a phone. He also was fairly confident that they weren’t in the blast area, judging by the time and their running pace. He and family members drove out of the city and waited for word.

Cindy and Katie Walls worked their way back to their planned meeting spot with the rest of their family, but they weren’t there. Cindy Walls said she noticed it was starting to get cold out, her body cooling down after having run 25 miles.

“Some guy comes up and says, ‘Here’s my cell phone and here’s my sweatshirt.’” Cindy Walls said she hesitated and the man said, “Take my sweatshirt, your lips are turning blue.”

And with the man’s cellphone, she contacted her husband. About 45 minutes later, they were reunited in a giant hug. “He was so happy,” Cindy Walls said. “It was unbelievable.”

John Walls said he figured his wife and daughter were safe, but he was still massively relieved when he saw them. “The most unbelievable day,” he said.

Cindy Walls, who has coached O’Connell to five Washington Catholic Athletic Conference cross country titles, wondered about the impact on running. “It’s a tragedy for marathons. A tragedy for America,” she said. ”The ramifications moving forward? You’ve got the Marine Corps marathon, New York City. It’s just sad.”