UTICA - A 24-year-old man died while running the 15 K Boilermaker Road Race. Sean O'Neill of Brooklyn died after collapsing during the race Sunday.

An autopsy Monday afternoon showed O'Neill died due to cardiac arrhythmia, according to Oneida County Coroner Mark Bentz. He said the underlying heart abnormality was undiagnosed.

The 2001 graduate of Whitesboro High School, near Utica, had been studying Japanese and had planned a trip to that country, said his friend Christine Scatko.

“He was the nicest guy ever,” Scatko said. “I don't think he had a mean bone in his body.”