may have been dead for up to six hours
before a security guard found her body in bed at around 4 p.m. London time on Saturday.
The five-time Grammy winner last spoke to her security team at 10 a.m. Saturday, telling them she was going to sleep. Rigor mortis had set in by the time she was found, suggesting she had been dead for several hours.
Sources tell Britain's Sun
newspaper that Winehouse, 27, had seen a doctor Friday night as part of a routine series of regular checkups, given her battle with addiction. The doctor saw nothing amiss.
Winehouse had been strong enough that same night to play a drum kit in her bedroom – so loud that neighbors complained.
Cause of death is not yet known; a toxicology report could take weeks to complete.
A police source tells PEOPLE there was no paraphernalia or sign of drugs in Winehouse's Camden home, which became the scene of makeshift memorials following news of the troubled singer's death.
Her father Mitch made an appearance at the Camden house Monday to thank fans who had built the tribute to his daughter in flowers and memorabilia. He said the family was "devastated and speechless."
"I can't tell you what this means to us. It really is making this a lot easier for us," he said of the tributes.
"Amy was about one thing, and that was love. Her whole life was devoted to her family and her friends, and to you guys as well," he told fans gathered in Camden Square.
Winehouse's friend and PR man Chris Goodman tells the Sun
that she had suffered setbacks in recent weeks in her battle against addiction.
"She was on the mend but she lapsed over the past month," he said. "Her death has come as a great shock. She was a fantastic talent and a sweet girl."
Monday, Winehouse's body was released to her family for funeral procedures. The official cause of death will be known in October.
Reporting by SIMON PERRY