Feeny said he immediately thought of the friends who had come to watch him in the race.

“It was terrifying,” he said. “I knew that I had asked a bunch of friends to come and watch me and they weren’t accounted for.”

Spectators at the finish line reported screaming children, blaring ambulances, and mass hysteria as people fled the scene.

Crawford said she saw other spectators tearing down the barricades separating the bystanders from the runners as they attempted to flee the finish line area.

“My friend and I just grabbed each other and stood there in absolute fear,” she said.

As Juarez returned to the scene of the explosion, he witnessed a chaotic mass of people, some frozen in confusion, others fleeing the streets.

“There were a lot of children crying, which really got to me,” he said. “It was very shocking, very out of place. It made me wonder why stuff like this happened.”

Harleen K. Gambhir ’14, who attended the race as a spectator, approached the finish line as the bombs exploded.

“I had a moment when I thought that everything might blow and there would be nowhere to run to,” she said. “A woman near me fell immediately and started screaming and crying.”

Many terrified Harvard runners and spectators expressed gratitude that they remained unscathed.

“I’m really thankful that I hadn’t run it a little faster,” Purcell said. “Unfortunately I couldn’t finish, but it could have been a lot worse.”

Juarez said he had considered going to the marathon’s finish line to take a photo, but ultimately he had decided against it.

“Had I made my way there a few minutes earlier I might have been a victim,” he said. “I thank God that that didn’t happen.”

With streets and nearby Massachusetts Bay Transportation Authority stations closed and taxis at a premium, Harvard affiliates encountered difficulty as they tried to make their way back to campus.

Feeny was among many who said they walked most or all of the way from Back Bay to Cambridge.