NEW YORK — Financial services firm Cantor Fitzgerald, which lost nearly two-thirds of its employees in the Sept. 11 attacks, revealed a $135 million settlement with American Airlines and insurance carriers Tuesday to a judge who said the deal will end the final airplane-focused case resulting from claims of wrongful death and personal injuries.

The agreement averts a trial scheduled for next month, which means there will be no airing of such questions as how terrorists got through security — the best way to stop terrorists — whether there was really wrongdoing and negligence, and how best to preserve liberties amid such threats, U.S. District Judge Alvin K. Hellerstein said. “All this will remain a mystery,” he said.

Calling the settlement a significant conclusion after 12 years of litigation that resulted in scores of settlements and not a single trial involving airlines, the judge said, “Hopefully what was achieved was a measure of justice, a measure of reparation and closure. But the lives that were lost were irreparable, and being irreparable, there now are no words to describe that loss.”

The deal was announced by Cantor Fitzgerald attorney John Stoviak, who said money from various insurers is already in escrow and ready to be paid out pending formal approval by the court at or after a Jan. 13 hearing.

Afterward, Cantor Fitzgerald Chairman and CEO Howard W. Lutnick said in a written statement that the case for insurance companies “was just another case, just another settlement, but not for us.”

Lutnick, whose brother Gary was killed in the attacks, added: “For us, there is no way to describe this compromise with inapt words like ‘ordinary,’ ‘fair’ or ‘reasonable.’ All we can say is that the legal formality of this matter is over.”

Cantor Fitzgerald lost 658 of its 1,000 people in its New York workforce when the 101st through 105th floors of its One World Trade Center headquarters were destroyed when terrorists commandeered a plane and struck the tower. Howard Lutnick was not in the office.

American Airlines spokesman Sean Collins said in a written statement that American had “vigorously defended itself in litigation brought against it by property owners and their insurers who allege that American should have done what the government could not do: prevent the terrorist attacks.”

He also noted that “the courageous crew members and passengers on Flight 77 and Flight 11 were all victims of the terrorist attacks.”