The death of a 15-month-old boy who was left alone for hours in a hot car in Connecticut last month has been ruled a homicide, the Connecticut state medical examiner's office said on Thursday.

After a six-week investigation, officials at the medical examiner's office determined that the boy, Benjamin Seitz, of Ridgefield, had died of hyperthermia because of environmental exposure.

In the early evening of July 7, the police in Ridgefield received a report about Benjamin's death from the staff of Danbury Hospital, where the boy's father, Kyle Seitz, had taken him after finding him left alone in his vehicle on a day when the temperature reached 88 degrees. Mr. Seitz, the police said at the time, was supposed to have dropped his son off at a day care center but instead drove to work at a Ridgefield computer technology company and left the boy in the car for "an extended period of time."

Stephen J. Sedensky III, the state's attorney in Danbury, said the investigation into Benjamin's death was continuing and declined to comment on whether any charges would be made.

Earlier this summer, Mr. Seitz and his wife, Lindsey Rogers-Seitz, set up a memorial blog and website for Benjamin, which seeks to raise public awareness about the dangers of leaving children alone in cars on hot days. On her blog, Ms. Rogers-Seitz wrote that she would not discuss "any theories of causation or responsibility" for what she called "these tragic events."