The blog— owned by the media conglomerate, Time Warner, but operated as a web-traffic-fueled fief in Hollywood — seemed to have sources everywhere: at Jackson’s mansion; in the ambulance; and in the corridors of the UCLA Medical Center. TMZ’s short post about the death was published at 5.20 pm Eastern time.

For more than an hour, TMZ was essentially the only outlet claiming that Jackson was dead. Television and newspaper journalists read the TMZ report but largely held off on repeating it, for fear of making a mistake. Still, the bulletin traversed the web with remarkable speed, creating a stark divide: on the internet Jackson was dead, and on TV he was still alive.

By early evening Jackson’s death had become the No. 1 story on newscasts worldwide. The intense, almost voyeuristic interest strained many Web servers, crashing AOL’s instant messaging service and even tripping up Google News for about half an hour. Tens of millions of viewers watched hastily arranged tributes to Jackson on nearly a dozen channels.

But it was TMZ that consistently led the news cycle, beginning with a report that paramedics had been called to the mansion. Shortly thereafter, before any TV networks had mentioned Jackson, the site said he had suffered an episode of cardiac arrest. “We are totally wired in this town,” Harvey Levin, the site’s editor-in-chief, said in a telephone interview on Friday.

The Jackson news was easily the biggest scoop in TMZ’s nearly four-year history. Kurt Andersen, a journalist and cultural critic, said the story was highly indicative of the evolving editorial practices that media outlets are grappling with. Among many journalists, “there’s still this residual but not yet vestigial instinct to think ‘Oh, it’s just TMZ, let’s wait for The Associated Press or The New York Times or The Los Angeles Times before we can say it’s true,” he said, adding: “I don’t think in, say, five years, that will be the case.”

The Jackson family said the time of death was 5:26 p.m. Eastern, several minutes after TMZ’s report, leading some to wonder whether the website looked accurate only in hindsight. Levin stood by the report, calling it 100 percent accurate.