Now, the death of a motorist killed by falling ceiling panels has created a full-fledged scandal, damaging the reputation of San Francisco's Bechtel and putting the company in legal jeopardy.

Privately held Bechtel led the joint venture that managed construction of the Big Dig, a maze of roadways beneath Boston's downtown and harbor. Ultimately, Bechtel's potential liability for the ceiling collapse could exceed the amount of money the company claims to have made off the project.

The Big Dig stands as one of the most ambitious -- and most controversial -- civil engineering projects in recent U.S. history.

It tore down an elevated freeway that cut through Boston's historic core, replacing the looming structure with tunnels. It spanned the Charles River with a new bridge, complete with soaring towers that mimic a Revolutionary War monument nearby. It connected the state's main east-west freeway to Logan International Airport via a tunnel beneath the harbor.

But the project took longer and cost far more than expected. Over roughly 20 years of planning, design and construction, costs swelled from initial estimates of $2.6 billion to $14.6 billion.

That convinced some state officials that they'd been gouged, setting in motion efforts to determine whether Bechtel and its joint venture partner, Parsons Brinckerhoff, were responsible for any of the cost overruns. Meanwhile, leaks in the tunnels eroded public confidence.

Under its contract, the liability of Bechtel and its joint venture partner for project losses is limited to $150 million. That's more than the roughly $130 million Bechtel has said that the joint venture made during the project's 20-year-history.

Since the July 10 accident that killed 39-year-old Milena Del Valle, who was on her way to the airport, the fury directed at Bechtel, Parsons Brinckerhoff and the Massachusetts Turnpike Authority, the tunnel system's operator, has reached a crescendo.

The Massachusetts attorney general has held open the possibility of criminal charges in Del Valle's death. The embattled head of the Massachusetts Turnpike Authority, Bechtel's client on the Big Dig, has stepped down under heavy pressure from Gov. Mitt Romney. Del Valle's family has signaled its intention to sue companies and government agencies connected to the project.

State and federal investigations into the collapse are under way and no one has yet been charged with responsibility for Del Valle's death. The liability limit might not apply if the Bechtel joint venture is found to have engaged in willful misconduct, gross negligence or fraud.

Bechtel has stood by its Big Dig work, which included drafting preliminary designs for the project and overseeing the many design and construction companies involved.

The company argues that the complicated nature of the project -- with multiple businesses designing and building the project's tunnels, freeway connectors and a new Charles River bridge -- make assessing blame difficult.

On some aspects of the work, "it may be the responsibility ends with the construction contractor," Bechtel spokesman Jonathan Marshall said. "On other things, the final responsibility may rest with the section design consultant. It's not as simple as pointing a finger at someone and saying, 'You're responsible.' "

Marshall said Bechtel's own examination of the accident had been hampered by the company's lack of documents detailing work on the collapsed ceiling.

Bechtel and its joint venture partners prepared preliminary designs for the Big Dig, performing about 25 percent of the total design effort, according to Bechtel's estimate. Specific designs for each segment of the project were drafted by other companies.

Bechtel's main role was serving as the project's management consultant, a job that New York attorney and construction expert Barry LePatner likened to an orchestra conductor, coordinating the work of multiple contractors and designers.

The San Francisco company said it completed the preliminary design for the ill-fated tunnel segment in 1992. State highway officials then picked another firm, Gannett Fleming, to draft more- detailed designs for the tunnel, including the ceiling. Modern Continental was hired for construction.

Throughout the project, individual contractors such as Modern Continental were responsible for quality control on the portions of tunnel or bridge they were building, according to Bechtel. The joint venture reviewed contractors' quality control programs before construction of each portion began.

Such a division of responsibility is common on large infrastructure projects, several construction experts said.

Lawyers versed in construction contracts say serious or intentional misconduct is very difficult to prove. In addition, companies in Bechtel's position -- management consultants coordinating the work on a large project -- rarely hold ultimate liability for the project's outcome, several lawyers said.

"The likelihood of a management consultant being found liable is very small," said Patrick Duffy III, a Los Angeles lawyer who specializes in construction projects at the Monteleone & McCrory law firm. "In that position, you typically have a lot of responsibility but very little liability."

Inspections since the accident have shown that other bolts used to anchor the tunnel's ceiling panels were slipping out of place. The state's attorney general said the companies working on the tunnel debated the adequacy of those bolts years ago.

But such debate, construction experts say, doesn't prove gross misconduct. It can even demonstrate the opposite -- that project managers were trying to find and fix potential problems.

"That kind of debate indicates there wasn't reckless disregard," said Scott Douglass, a partner in the Farella Braun & Martel law firm in San Francisco who specializes in construction projects.

A Big Dig memo that surfaced last month, written by a project supervisor, said the Bechtel joint venture and Modern Continental, the company that built the ill-fated tunnel, were warned years ago that bolts holding the ceiling panels in place might not last.

But Modern Continental last week claimed that the memo, initially obtained by the Boston Globe, was a fake. The memo's author insists it's genuine.

Meanwhile, the turnpike authority two weeks ago told Massachusetts lawmakers that it had $800 million in insurance that could be used to pay for Big Dig inspections, repairs and lawsuits, Boston papers reported. A turnpike authority spokeswoman did not return calls seeking comment.

Earlier this year, Massachusetts Attorney General Tom Reilly demanded that the joint venture refund about $108 million. Settlement negotiations were under way at the time of Del Valle's death but have since been suspended.

A Reilly spokeswoman said investigators are trying to determine whether the joint venture committed the kind of serious or intentional misconduct necessary to lift Bechtel's liability limit, among other issues.

"We will follow the evidence where it takes us," said spokeswoman Meredith Baumann. "That means everything is on the table."