The singer was among 20,000-plus competitors taking part in the annual race in Boston, Massachusetts, and had completed the race just 11 minutes before two explosions ripped through the crowds close to the finish line.
MCIntyre burst into tears during a radio interview on Tuesday morning (16Apr13), as he relived the horror, and he admits he's still having trouble coming to terms with the tragedy, which left three people dead and more than 150 injured.
On Thursday (18Apr13), as news outlets suggested authorities were trying to identify two men suspected of involvement in the bombings, MCIntyre took to his Twitter.com page and wrote, "I don't wanna watch but I do. I don't wanna hear about it but I have to. I wish I didn't care who did it but I can't wait 'til they get 'em."
The pop star then tried to lighten the mood by revealing his marathon efforts had helped to boost donations for an Alzheimer's disease research charity, while he also shared a photo of him mid-way through Monday's race, giving his elderly mother a peck on the cheek.
He adds, "On a 'hope' note, u guys raised $40,000 to fight Alzheimer's! And this kiss with my mom at 23 miles was worth more!"