I'm not sure if it was the road race or triathlon, but two riders crashed 1 literal metre from the finishing line and one got up and ran over the line without his bike just as the third rider passed the line?
The other incident is entirely more dramatic. An Iranian rider, Bahman Golbarnezhad, died after a crash in the first part of the race. Apparently, he suffered neck trauma and died in the hospital.
http://www.bbc.com/sport/disability-sport/37398333
BBC on Bahman Golbarnezhad's death. Condolences to family and friends.
Updated - According to the IPC, Golbarnezhad was involved in a crash at around 10:40 local time on the first section of the Grumari loop, a mountainous stretch of the course.
He received treatment at the scene and was in the process of being taken to the athlete hospital when he suffered cardiac arrest.