updated 04/20/2013 AT 10:00 AM ET
•originally published 04/20/2013 AT 3:05 PM ET
Even as he huddled with his wife in Watertown, Mass., on Friday, David Henneberry never imagined he’d come face to face with the alleged Boston bomber.
But that’s exactly what happened around dusk on Friday evening.
As tanks and SWAT vehicles rolled through the streets and cops went door to door in search of Dzhokhar Tsarnaev, Henneberry was outside smoking a cigarette when he noticed something amiss with the power boat he keeps parked in his driveway.
“He noticed that the tarp that had been covering his boat all winter was slightly flapping,” his stepson Robert Duffy tells PEOPLE. “So he went over to take a closer look and noticed that one of the restraining straps had been cut and that there was some blood on the blue tarp.”
Alarmed, Henneberry grabbed a step ladder and climbed up the boat’s side to take a closer look, where he made a shocking discovery.
“When he flipped a section of the loose tarp off, he saw a pool of blood and what appeared to be a crumpled body,” says Duffy.
Henneberry called 911 and within minutes police swarmed their home.
Over the next several hours, as the crackle of gunfire sounded periodically throughout the neighborhood, his mother and stepfather were “terrified.”
“I couldn’t get them on their home phone or on their cell phones. I was crying and thinking, ‘This can t be how it ends,’ ” recalls Duffy, who wasn’t with them at the time. “Finally, my sister called and said our mother had used someone s phone and called her and that they were OK. I cried with joy.”
Hours after Tsarnaev’s dramatic capture Duffy was still reeling.
“I am still shocked at everything that happened and how close to home it hit on so many levels,” he says. “I see a very sick individual who has caused a lot of harm to thousands of lives and families – and that will last decades.”