The nail in the well's coffin came in the form of a lethal shot of cement.
BP pumped fresh cement from the top of the blown out well in the Gulf of Mexico, sealing it off and laying the path for a planned permanent kill later this month. The cement is the "kill" phase of the static kill.
"This is not the end, but it will virtually assure us there will be no chance of oil leaking into the environment," retired Coast Guard Adm. Thad Allen, who oversees the government's spill response, said today.
On Wednesday, crews poured heavy mud down the broken wellhead, pushing the oil back to its underground source -- the first part of the operation.
But the official death knell, according to the government, will come from a "bottom kill," where mud and cement are injected through an 18,000 foot relief well that will intersect with the old well. This will plug the reservoir 13,000 feet beneath the seabed, bookending the runaway well with impenetrable cement columns hundreds of feet long.
BP engineers first corked the well using a temporary capping system called a stacking cap last month, blocking the oil that had been spewing since the Deepwater Horizon rig exploded off of Louisiana's coast on April 20, killing 11 workers and launching the greatest offshore oil spill in history.
The well may be technically dead, but the spill is not over. Scientists from around the nation are challenging a government report released Wednesday that claimed 75 percent of the oil, 207 million gallons, was cleaned up by man or mother nature.
Professor Pedro Alvarez, chair of Rice University's civil and environmental engineering program, said that just because 75 percent of the oil is unaccounted for does not mean it is not there.
"I believe that most of it, at least 50 percent of the amount released is probably still in the water," Alvarez said.
The government does acknowledge that at least 25 percent of the oil is still lurking in the water, nearly 53 million gallons of it. That is the equivalent of five Exxon Valdez spills.
"We don't know for example how this will...accumulate through the food chain and what effect it may have on the next generation of marine life or wildlife," said Alvarez.
Local Leaders: Oil Still in Water and Marshes
As skimming boats and cleanup crews leave the spill scene, local leaders have echoed the claims of scientists that the oil is still out there and that they still need help.
"When the storm kicks up, any kind of wind, the oil mixes up. Early in the morning, late in the evening, it's on the surface. You've got to skim it then or it ends up in the marsh," Nungesser said.
Clutching a jar full of dark black crude, Nungesser said that the oil is still damaging the fragile marshes.
"Make no mistake, there's large areas that are totally destroyed, and the greenery is completely dead," Nungesser said.
He said that cleanup crews over the weekend found thousands of dead fiddler crabs as well as dead fish and oiled birds.
"As of last night, we have 187 sea turtles that have come in for rehabilitation and care," Calhoun said. "They're found floating around in patches of oil, so to me that would be the evidence that oil is still out there."
Today, ABC News went to the marshland and the oil was easy to find, hundreds of gallons floating in the water, a ribbon of black. Cleanup workers said that they have spent days in the marshes sucking the oil from the surface of the water with giant vacuums.
They toil in record heat, but the hardest thing to swallow for crew chief Jeff Masters was the sound of politicians declaring victory.
"I don't see no end in sight, I mean look at this, it's terrible," Masters said. "I heard those people on TV yesterday saying, you know, it's almost over, they are crazy."
Federal Officials said that it could take a day for the cement pumped into the well to be blown dry. It will take at least five more days for crews to finish drilling the relief well.
Federal officials said they won't leave the Gulf until they restore it to its former state. Gulf residents and scientists say doing that could take years.