Donal Conlon was woken by the sound of gunfire about a block down Mount Auburn Street from his home in Watertown near Boston early on Friday morning, shortly after midnight.
The noise was so loud the bangs sounded like they were coming from his basement, he said. The 40-year-old Sligo man, a software consultant, decided to walk down the front steps to his house to see what was going on.
What he saw in front of him was "like a war-zone," Mr Conlon told The Irish Times. Heavily armed police and other law enforcement agents were "flying everywhere" in full riot gear. "I have never seen such an exhibition of police in full military gear," he said.
He recalled the 15-minute gun fight that led to the death of the suspected Boston Marathon bomber Tamarlan Tsarnaev and sent his younger brother Dzhokhar Tsarnaev on the run, triggering a 20-hour manhunt in the area.
During the firefight, a man with a Middle Eastern complexion walked towards Mr Conlon wheeling a bicycle. Unconnected with the violence, the man was in tears, distraught at the events unfolding around him.
Not knowing who the two men were, police approached them pointing assault rifles into their faces. They were told to lie down on the ground, handcuffed and frisked.
A short time later, a neighbour popped his head out the front door of his house and vouched for Mr Conlon. The Irish man was released after 15 minutes and told to go back inside his home.
The Middle Eastern-looking man was detained for longer, up to an hour, because he resembled one of the two Chechen brothers. Once released, Mr Conlon tried to calm him, telling him to stay with him until the fight had ended.
"He was crying and sobbing. I told him he was not going anywhere," said Mr Conlon who has been living in the United States for 15 years and in the Watertown for four years.
Mr Conlon watched the five to 10 minute gun battle from his home.
The firefight had started when one police officer came across two cars driven by the Tsarnaev brothers, Watertown Police Chief Edward Deveau told CNN in an interview yesterday.
The brothers had been chased by police from nearby Cambridge where they were suspected of killing Steve Collier, a campus police officer in Massachusetts Institute of Technology, across the river from the city of Boston.
In Watertown, the officer was told not to approach the brothers and to wait for back-up. Before it came, the brothers left their cars and started shooting at the police car. Five other officers arrived and the gun fight began.
Mr Deveau estimated that more than 200 shots were fired in a battle that was captured on video from different angles by nearby residents. The videos were on the television news within hours. The brothers also threw three explosives at the officers, including a pressure cooker bomb.
Tamerlan started walking towards the police while shooting. After running out of ammunition, an officer tackled him and as officers were handcuffing him in the street, Dzhokhar drove a black SUV at them.
The officers dived out of the way, said Mr Deveau, and Dzhokhar drove the car over his brother, dragging him a short distance down the street. Tamerlan was pronounced dead at a nearby hospital at 1.35am. Dzhokhar later abandoned the SUV and fled on foot.
The younger of the two brothers was discovered around 8pm on Friday, holed up in a boat sitting in the back garden of a house on Franklin Street, about a kilometre away - roughly a 15-minute walk - from Mr Conlon's house.
At 9pm, Mr Conlon and his fiancée, who had been stuck at home during the manhunt, went to Conley's, one of two local Irish bars in Watertown where customers swapped their stories of the dramatic events of the day in their neighbourhood.
"At the time [of the gun fight] I wasn't worried," said Mr Conlon. "It was just so surreal."