It isn't clear whether Mr. West's investigation would have yielded enough evidence to charge BP with a felony, had he been allowed to continue. Moreover, the EPA wouldn't necessarily have been able to secure the damages from BP, even if it had obtained a verdict against the company in a trial.

Nelson Cohen, the U.S. attorney for Alaska, said that opting for the $20 million fine was "a judgment call" his office made. "It's not my job to take every nickel from a defendant when they have done something wrong," he said. "Our job is to come up with what we feel is fair and just." EPA officials say they agree with the final resolution of the case. EPA officials say the $20 million was among the highest fines ever won under the Clean Water Act.

In response to a summary of Mr. West's complaints provided to BP by The Wall Street Journal, BP said in a statement that the EPA and Justice Department "received BP's full cooperation in their Alaska investigation." BP added: "We read with interest that after a 17-month investigation, West and other investigators could not 'realistically charge' BP with a felony."

Mr. West, who retired from the EPA on Oct. 29 and has now gone to work as lead investigator for environmental group Sea Shepherd, was looking into two pipeline spills at BP's Prudhoe Bay facilities in Alaska in 2006. He says the probe ended after Ronald Tenpas, a career prosecutor for the Justice Department, was appointed assistant attorney general for the environment and natural resources in May 2007.

Mr. West says that in August 2007, at a meeting of federal officials on the case in Anchorage, a prosecutor asked whether he had enough evidence to charge BP with a felony. Mr. West says he didn't at that point, but needed another year or so to go through the evidence that EPA and Federal Bureau of Investigation agents had gathered. While he was given 17 months to investigate after the March 2006 spill, Mr. West says such probes typically take two to four years, and other federal law-enforcement officials confirm that.

Mr. West alleges that prosecutors told him it wasn't in the government's interest to continue the investigation if it could settle with BP on a misdemeanor. Following the meeting, Mr. West says, Karen Loeffler, the criminal chief in the U.S. attorney's office, told him "the decision to settle now was made by Ron Tenpas."

Mr. Cohen, speaking on Ms. Loeffler's behalf, says she "flatly denies" making that statement. He adds that his office acted independently in resolving the case. "I was never pressured in any way, shape or form in how to handle the case," Mr. Cohen says.

Mr. Tenpas, who supervises environmental cases from Washington, said he was kept apprised of the investigation, but "I vehemently disagree and deny" that he ended it. "It was a decision I concurred with, but the decision was not mine," Mr. Tenpas said.

A Justice Department spokesman said the decision was made by Mr. Cohen, after consultation with prosecutors in both Alaska and Washington who were assigned the case.

Mr. West says his inquiry began in July 2005 -- before the actual spills -- after some BP engineers told him that a pipe rupture and leaks were inevitable, and that their warnings had been repeatedly ignored. The engineers were steered to him by Charles Hamel, a former oil-tanker broker who serves as a conduit for oilfield workers' complaints in Alaska. In March 2006, a corroded line broke, spilling about 200,000 gallons of crude on the tundra. In August 2006, a spill of about 1,000 gallons took place at another corroded line nearby. No injuries resulted from either spill. BP, which in its plea agreement admitted to negligence in not preventing corrosion on oil-transit lines at Prudhoe Bay, then ordered almost the entire field shut down to repair corroded pipes. The company has said it replaced miles of the lines at the field.

The EPA probe kicked into high gear after the spills, with as many as a dozen criminal investigators from the agency, the FBI and the state of Alaska, Mr. West says. He says there was an effort early on among EPA officials to look at possible illegal behavior, based on what he described as worker complaints that management repeatedly ignored warnings that the corrosion problem needed to be addressed. EPA officials said last week that such behavior was never proven. BP said that "we have no record that any concerns about corrosion leading to an oil transit-line breach...were communicated to BP by BP Alaska workers."

At the Anchorage meeting of investigators in August 2007, Mr. West says he asked for a year's more time, then six months and finally three months, when he was told by officials of the U.S. attorney's office that there was no reason to continue the probe. "He had more theories on what he wanted to pursue, but those already had been pursued," Mr. Cohen says.

A person familiar with the investigation said Mr. West's team still had a lot of work to do before they could determine whether the case warranted any felony charge. For example, this person said, investigators hadn't interviewed a number of people at BP who had knowledge of the company's corrosion program in Alaska.

Mr. West says Mr. Cohen's own prosecutors had been discussing the case as a potential felony, depending on what the evidence turned up. A Justice Department spokesman said the agency does not comment on what prosecutors discuss internally.

On Oct. 15, 2007, Mr. West says, he attended a settlement meeting with BP lawyers at the U.S. attorney's office in which Mr. Cohen offered to settle the case for a $20 million fine. An EPA analysis two weeks earlier proposed two options of $58.5 million or $89.8 million in the misdemeanor case. EPA officials confirm the calculations were made. Mr. Cohen said they "discussed what a proper penalty should be. This is what we decided was a fair and just result."

BP said in its statement that it "admitted that its processes and systems for monitoring Prudhoe Bay oil-transit lines were inadequate," and "that negligence on the company's part resulted in the March 2006 spill."

Write to Jim Carlton at