Tony Hsieh, who developed Zappos into a billion-dollar internet shoe store and formulated an influential theory about corporate happiness, deliberately locked himself in a shed moments before it was consumed by the fire that would kill him.

Last November, Mr. Hsieh was visiting his girlfriend, Rachael Brown, in her new $1.3 million riverfront house in New London, Conn. After the couple had an argument about the messiness of the house, Mr. Hsieh set up camp in the attached pool storage shed, which was full of foam pool noodles and beach chairs.

Those details appeared in reports released Tuesday by New London fire and police investigators, the first law enforcement accounts of the incident. They said Mr. Hsieh could be seen on a security video from Nov. 18 looking out the shed door about 3 a.m., even though no one was about. Light smoke rose behind him.

When Mr. Hsieh closed the door, there was the sound of the door lock latching and a deadbolt being drawn.

The entrepreneur, 46, was traveling with a nurse. He planned to leave before dawn for Hawaii with Ms. Brown, his brother Andrew, and several friends and employees, according to the police report. While in the shed, he asked to be checked on every 10 minutes. His nurse, who was staying in a hotel, said this was standard procedure with Mr. Hsieh.

Investigators said they didn’t know exactly what had started the fire, partly because there were too many possibilities. Mr. Hsieh had partly disassembled a portable propane heater. Discarded cigarettes were found. Or maybe the blaze erupted from candles. Investigators said his friends had told them that Mr. Hsieh liked candles because they “reminded him of a simpler time” in his life.

A fourth possibility is that Mr. Hsieh did it on purpose.

“It is possible that carelessness or even an intentional act by Hsieh could have started this fire,” the fire report said. The report added that Mr. Hsieh may also have been intoxicated, noting the presence of several Whip-It brand nitrous oxide chargers, a marijuana pipe and Fernet-Branca liqueur bottles.

The exact role of drugs or alcohol that night is likely to remain unclear. Dr. James Gill, Connecticut’s chief medical examiner, said in an email that “autopsy toxicology testing is not useful” if the victim survives for an extended period. A final report is pending.

Firefighters who broke down the door found Mr. Hsieh lying on a blanket. He was taken to a nearby hospital and then airlifted to the Connecticut Burn Center, where he died on Nov. 27 of complications from smoke inhalation.

Mr. Hsieh’s death shocked the tech and entrepreneurial worlds because of his relative youth and his writing on corporate happiness. Zappos was a star of the early consumer internet, helping convince the cautious that buying online held few perils. Mr. Hsieh became chief executive in 2001, promoting to all who would listen the notion that companies should try to make their customers as well as their employees happy. He relocated Zappos from the Bay Area to Las Vegas.

Amazon bought Zappos for $1.2 billion in 2009. The next year, Mr. Hsieh published “Delivering Happiness,” a best seller. “Our goal at Zappos is for our employees to think of their work not as a job or career, but as a calling,” he wrote.

Mr. Hsieh remained at Zappos but turned his attention to a civic project to revitalize downtown Las Vegas. Many investments and many years later, the project was at best an incomplete success. In the last year or so, Mr. Hsieh concentrated on Park City, Utah, where he spent tens of millions of dollars buying properties and became so manic that friends said they had discussed an intervention. Few outsiders knew that he had quietly left Zappos.

On the night of the fire, according to police interviews, Mr. Hsieh was despondent over the death of his dog the previous week during a trip to Puerto Rico. He and Ms. Brown had a disagreement that escalated, at which point Mr. Hsieh retired to the shed. An assistant checked with him frequently, logging the visits with Post-it notes on the door. Mr. Hsieh would generally signal that he was OK.

As the group prepared to depart in the middle of the night for the airport, Mr. Hsieh asked for the check-ins to be every five minutes. But four minutes were all it took for the fire to become deadly. Attempts by those in the house to break down the locked door were unsuccessful. Three Mercedes-Benz passenger vans arrived to take the party to the airport about the same time that firefighters arrived.

Ms. Brown, an early Zappos employee, did not return calls for comment. A family spokesman also did not respond to a message for comment.

Firefighters were regular visitors to the house in mid-November. On Nov. 16, they were summoned at 1 a.m. by a smoke detector that was wired into a security company. A man who answered the door said the alarm had been set off by cooking, according to department records.

The firefighters left but returned minutes later, prompted by another smoke detector. “On arrival found nothing showing and a male stating again that there was no problem,” Lt. Timothy O’Reilly wrote in a summary of the call. Firefighters said they had entered to take a look around.

Lieutenant O’Reilly and his colleagues found smoke in the finished basement, along with “melted plastic items on the stovetop along with cardboard that was hot to the touch,” which were apparently plastic utensils and plates. They also found a candle burning in “an unsafe location” and extinguished it. While the smoke in the basement dissipated, the firefighters offered fire safety tips.

The investigators’ report also recounted an episode early in the evening of Nov. 18. Mr. Hsieh’s assistant checked on him in the shed and noticed a candle had fallen over and was burning a blanket. The assistant asked Mr. Hsieh to put out the flame, and the entrepreneur did.