By Andrew Longstreth 

Nov 15 (Reuters) - Lawyers for two BP Plc employees who were charged with manslaughter on Thursday in the Deepwater Horizon disaster said the U.S. government had unfairly targeted their clients.

Robert Kaluza and Donald Vidrine, the two highest ranking BP supervisors onboard the rig in the hours before the disaster, were innocent of the charges against them, the lawyers said.

Earlier on Thursday, the government alleged that "negligent and grossly negligent" conduct by Kaluza and Vidrine led to the explosion aboard the Deepwater Horizon rig, the deaths of 11 workers and the release of millions of barrels of oil into the Gulf of Mexico.

On April 20, 2010, Kaluza and Vidrine were aware that a drill pipe inserted into the Macondo well to test its pressure showed that the well was not secure, the government said in an indictment. They then failed to alert engineers onshore to the problem and accepted "illogical" explanations from members of the rig crew as to why pressure in the well was building, according to the indictment. Later that evening, the rig exploded, killing 11 men onboard.

In statements, lawyers for the two men said their clients were being wrongly targeted.

"After nearly three years and tens of millions of dollars in investigation, the Government needs a scapegoat," said Shaun Clarke and David Gerger, attorneys for Kaluza. "No one should take any satisfaction in this indictment of an innocent man. This is not justice."

Vidrine's attorney said that the government had "exercised exceedingly poor judgment" in charging his client.

"It is almost inconceivable that any fair-minded person would blame this hardworking and diligent man for one of the most catastrophic events in the history of the oil business," said the attorney, Bob Habans.

Both Vidrine and Kaluza are veterans of the oil business, according to their lawyers. Vidrine has over 39 years experience while Kaluza, who joined BP in 1997, has 44.

The two each face 11 counts of involuntary manslaughter, 11 counts of seaman's manslaughter and one count of Clean Water Act violations.

Involuntary manslaughter is a broad statute covering individuals whose reckless conduct leads directly to the loss of life. Seaman's manslaughter is reserved for those employed on ships whose misconduct results in death.

Generally to prove manslaughter at a trial, prosecutors have to show that the defendant's conduct was more than mere negligence, legal experts said.

"It becomes a very difficult case for both defense lawyers and prosecutors," said Ed Little, a defense attorney who is not involved in the BP case. "It becomes a rhetorical battle."

In addition to the legal standard of manslaughter, another key aspect to the case could be what other factors could be to blame for the disaster.

In his statement, Vidrine's lawyer said that numerous investigative bodies had blamed many other individuals and factors. "Among many causes identified by these investigations were the failure of negligently designed cement at the bottom of the well, the failure of the blowout preventer, and the failure of others to monitor and control the well," he said.

BP on Thursday agreed to pay the U.S. government $4.5 billion and to plead guilty to felony misconduct in the disaster.

A third individual, a former senior BP executive, was charged with misleading the U.S. Congress as it investigated the spill.

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