One of the Detroit Marathon deaths ruled: natural causes

According to the Free Press:

Rick Brown, 65, of Marietta, Ohio, died of natural causes when he collapsed during the half-marathon, an autopsy concluded. Autopsy results still are pending in the deaths of 36-year-old Daniel Langdon of Laingsburg and 26-year-old Jon Fenlon of Waterford.

They article specifically addressed the internet speculation about poison:

Because the three runners collapsed in such a short time this year, the deaths sparked some speculation in Internet postings as to whether the men may have been given tainted water as they ran. Brown's autopsy included toxicology screening, which was negative for alcohol, illegal drugs, prescription medications and poisons.