However, as a whistleblower previously told 60 Minutes, there was an accident at the rig a month or more prior to the April 20th explosion:

[Mike Williams, the chief electronics technician on the Deepwater Horizon, and one of the last workers to leave the doomed rig] said they were told it would take 21 days; according to him, it actually took six weeks.

With the schedule slipping, Williams says a BP manager ordered a faster pace.

"And he requested to the driller, 'Hey, let's bump it up. Let's bump it up.' And what he was talking about there is he's bumping up the rate of penetration. How fast the drill bit is going down," Williams said.

Williams says going faster caused the bottom of the well to split open, swallowing tools and that drilling fluid called "mud."

"We actually got stuck. And we got stuck so bad we had to send tools down into the drill pipe and sever the pipe," Williams explained.

That well was abandoned and Deepwater Horizon had to drill a new route to the oil. It cost BP more than two weeks and millions of dollars.

"We were informed of this during one of the safety meetings, that somewhere in the neighborhood of $25 million was lost in bottom hole assembly and 'mud.' And you always kind of knew that in the back of your mind when they start throwing these big numbers around that there was gonna be a push coming, you know? A push to pick up production and pick up the pace," Williams said.

Asked if there was pressure on the crew after this happened, Williams told Pelley, "There's always pressure, but yes, the pressure was increased."

But the trouble was just beginning: when drilling resumed, Williams says there was an accident on the rig that has not been reported before. He says, four weeks before the explosion, the rig's most vital piece of safety equipment was damaged.

As Bloomberg reports today, problems at the well actually started in February:

BP Plc was struggling to seal cracks in its Macondo well as far back as February, more than two months before an explosion killed 11 and spewed oil into the Gulf of Mexico.

It took 10 days to plug the first cracks, according to reports BP filed with the Minerals Management Service that were later delivered to congressional investigators. Cracks in the surrounding rock continued to complicate the drilling operation during the ensuing weeks. Left unsealed, they can allow explosive natural gas to rush up the shaft.

“Once they realized they had oil down there, all the decisions they made were designed to get that oil at the lowest cost,” said Peter Galvin of the Center for Biological Diversity, which has been working with congressional investigators probing the disaster. “It’s been a doomed voyage from the beginning.”

***

On Feb. 13, BP told the minerals service it was trying to seal cracks in the well about 40 miles (64 kilometers) off the Louisiana coast, drilling documents obtained by Bloomberg show. Investigators are still trying to determine whether the fissures played a role in the disaster.

***

The company attempted a “cement squeeze,” which involves pumping cement to seal the fissures, according to a well activity report. Over the following week the company made repeated attempts to plug cracks that were draining expensive drilling fluid, known as “mud,” into the surrounding rocks.

BP used three different substances to plug the holes before succeeding, the documents show.

“Most of the time you do a squeeze and then let it dry and you’re done,” said John Wang, an assistant professor of petroleum and natural gas engineering at Penn State in University Park, Pennsylvania. “It dries within a few hours.”

Repeated squeeze attempts are unusual and may indicate rig workers are using the wrong kind of cement, Wang said.

In other words, the well may have lost integrity in February, and never been properly repaired. If cracks in the well were never fully sealed, then the well may have been unstable starting in February and continuing until the April 20 explosion. (There is substantial evidence that there are cracks in the well now.)

Bloomberg continues:

In early March, BP told the minerals agency the company was having trouble maintaining control of surging natural gas, according to e-mails released May 30 by the House Energy and Commerce Committee, which is investigating the spill.

***

While gas surges are common in oil drilling, companies have abandoned wells if they determine the risk is too high.

***

On March 10, BP executive Scherie Douglas e-mailed Frank Patton, the mineral service’s drilling engineer for the New Orleans district, telling him: “We’re in the midst of a well control situation.”

The incident was a “showstopper,” said Robert Bea, an engineering professor at the University of California, Berkeley, who has consulted with the Interior Department on offshore drilling safety. “They damn near blew up the rig.”

In other words, not only is it possible that the well casing has been unstable since February, but BP may have ignored standard drilling practices by failing to abandon the well when the natural gas began surging too violently.

Sure, the rig didn't actually catch fire and sink until April, but cracks in the well and dangerous natural gas surges may mean that BP actually started losing containment of the well much earlier.

Note 1: These new facts also add to the massive evidence that BP has been criminally negligent.