Before long, however, Mr. Brennan said that the crash was the responsibility of USAir alone -- a judgment, prosecutors later contended, based not on the circumstances of the crash, but on his concern for U.S. Aviation's bottom line.

There was a wide disparity in the way U.S. Aviation had hedged its coverage for the two companies. In USAir's case, the insurer had sold off its risk, so if the airline was considered entirely responsible, the cost to U.S. Aviation would be minimal. But U.S. Aviation had retained some of the risk on Ogden Allied's policy; if the security company bore a share of the blame, U.S. Aviation would have to pay out as much as $7.5 million at a time its underwriting losses were growing.

That fact, court documents and trial testimony indicate, was known only to a few U.S. Aviation executives. To shift costs away from the company, prosecutors in the mail fraud case asserted, U.S. Aviation concealed facts about Ogden Allied's security lapses from USAir and other insurers and pressured them through misleading statements to accept full responsibility for the crash.

Mr. Clark, the insurer's chairman, said that Mr. Brennan and the company had simply judged, based on years of experience, that the accident was USAir's fault.

''It is clearly an example of the system gone wrong,'' Mr. Clark said of the guilty verdict this summer in Brooklyn. Edward A. McDonald, a lawyer representing Mr. Brennan, said his client continues to maintain that he is innocent of any wrongdoing.

USAir, however, had expressed concerns from the start. Soon after the crash, according to trial testimony, the airline told U.S. Aviation that it was worried that it would not be treated fairly because the insurer also represented Ogden Allied.

U.S. Aviation reassured the airline, and USAir and Ogden Allied then agreed not to blame each other publicly to avoid strengthening the hand of plaintiffs' lawyers, according to court documents and trial testimony. Although they would present a unified defense, the insurer also promised a private meeting after all lawsuits were settled to share evidence about lapses that led to the crash. With that information, the parties it represented could pay their fair share. At the time, however, USAir did not know that between them, U.S. Aviation and Ogden Allied lawyers had already estimated that the security company bore up to a third of the blame for the crash, according to court records.