A family member called the Mission Bay Dentistry office to check on the boy. That's when Dr. Dennis Sierra, 42, ran out with some of his employees to find his son, Andres, not breathing.

They took the boy out of the maroon Ford Explorer, which had all the windows up and was parked on the north side of the Mission Bay Office Center, and started performing CPR.

"This is terrible tragedy. It was an accident," said Sierra's attorney, Michael Salnick outside the hospital where the boy was pronounced dead at 1:27 p.m.

Salnick added that the toddler's father is "grieving beyond the definition of the word 'grief'.

"He was a son whose father loved him very much."