(CBS) -- CBS News has learned that BP is set to embark Thursday on the fifth day of a little-known subsea mission under Coast Guard supervision to look for any new oil leaking from the Deepwater Horizon disaster.
The BP oil rig exploded in 2010, killing 11 workers and sending more than 7 million gallons of oil gushing into the Gulf of Mexico for three months before it was capped.
In September, a new oil sheen was spotted about 50 miles off the Louisiana coast. Tests confirmed the oil came from the infamous Macondo well underneath the Deepwater Horizon. BP's underwater vehicle observed oil seeping from the well's containment dome and, after a remote operation, declared the leaks plugged on October 23. The company and the Coast Guard said it wasn't feasible to clean up the slick, and that it didn't pose a risk to the shoreline.
But more oil continues to surface. Slicks and sheens of varying sizes and shapes have been documented by satellite photos, as well as aerial video recorded by the non-profit environmental group "On Wings of Care." It's suspected that an unknown amount of oil trapped in the containment dome, and in the wreckage and equipment from 2010, could be seeping out.
Rep. Ed Markey, D-Mass., helped lead the original investigation of BP after the Deepwater Horizon exploded, and says it's deja vu: BP is not turning over videos and information requested by Congress.
"My concern is that substantial amounts of oil could still be leaking from the wreckage," Markey told CBS News.
Last month, BP pleaded guilty to more than a dozen felonies from the 2010 disaster, including lying to Congress about how much oil was really pouring into the water.
Markey says BP is now repeating its stonewalling behavior of two years ago. For more than two months, Markey and Rep. Henry Waxman, D-Calif., have been asking BP for underwater video and information such as the size of the slicks and how much oil could be trapped, but BP has said it will not provide the information due to pending investigations and litigation.
"Back in 2010, I said BP was either lying or incompetent. Well, it turns out they were both," says Markey. "This is the same crime scene, and the American public today is entitled to the same information that BP was lying about in 2010 so that we can understand the full dimension of the additional environmental damage."
BP spent a fortune after the 2010 disaster -- on ads to improve its image. It also spent $18 billion on cleanup and victims, and $4.5 billion more to settle criminal charges.
The Coast Guard canceled an interview with CBS News at the last minute on Wednesday. BP also declined to be interviewed but told us in a statement, "The Macondo well and its associated relief wells are secure." BP also says it will work with the Coast Guard "on any further steps, as needed, to address the results" of this week's survey of the wells and wreckage where oil from 2010 could still be trapped.
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