A sky-diving instructor and his student plunged more than 9,000 feet to their deaths after their parachutes failed to open, authorities said.

Sunday's deaths of Donald Batchelor, 34, and Zaine Oller, were under investigation, authorities said.Batchelor, a sky-diving instructor with 10 years' experience, was strapped to Oller's back in a formation in which the instructor holds the controls to their common harness and parachute, Metro-Dade police spokeswoman Lucy Fitts said.

A reserve parachute also failed to open, authorities said.