Bill Richard is a leader in a local community group, and an avid runner and bicyclist. Cunningham said he believed his friend didn't run Monday's race because he has an injury, and Richard wasn't listed as a runner on the marathon's website.
Denise Richard works as a librarian at the Neighborhood House Charter School, where Martin was a third-grader and Jane attends first grade.
Counselors were being made available Tuesday to staff and students, according to school spokeswoman Bodi Luse, who said the whole community was devastated.
"I just can't get a handle on it," Cunningham said of the boy's death. "In an instant, life changes."
Associated Press writers Jay Lindsay and Pat Eaton-Robb contributed to this report.