"Despite my team working around the clock to give me every chance to make the starting line, on this occasion it will not be possible", the 26-year-old said.
And on the eve of the 2018 marathon, the mayor believes the tragedy has united the city.
22 locals from Las Vegas have made their way to the Northeast to run the Boston Marathon, in honor of those who lost their lives too soon. Hasay, who is part of the Nike Oregon Project, finished in third place a year ago.
The run will be noticeably different for him this year.
After sitting out the past two Boston Marathons (due to the Olympics in 2016 and an injury last year), the Nike athlete has high hopes for Monday's race.
The question will be how much longer Kiplagat, now 38, can maintain her winning form.
Captain Truchard says he's looking forward to running alongside those who are not only Vegas Strong, but also Boston Strong.
Shalane Flanagan becomes the first USA woman since 1977 to win NYC Marathon.
More recently Rupp has become only the second USA runner to break the hour mark for the half-marathon.
Meanwhile, Kirui aims to repeat last year's success.
The field includes two other estimable Ethiopian past winners - Lemi Berhanu, who took the title two years ago, and Lelisa Desisa, who won in 2013 and 2015, making a widely acclaimed gesture after the first victory when he returned his medal to the city to honour those killed and injured in the bombings that disfigured the later stages of that race.