INDIANAPOLIS —  An airline passenger died in the restroom during a flight from Tokyo and was not found until the cleaning crew boarded the plane after it landed, a federal lawsuit contends.

The passenger, Taisuke Matsuo, 66, apparently had a heart attack on an American Airlines flight to Chicago — the first leg of a trip home to Indianapolis, according to the lawsuit filed Monday by his wife, Carolyn D. Watts.

The lawsuit accuses American Airlines of negligence and seeks damages of about $150,000.

After the plane landed at Chicago O'Hare International Airport on April 13, 2005, passengers and flight crew disembarked and the jet was taken to another gate for cleaning. Workers then discovered the bathroom was locked from the inside and found Matsuo's body — about two hours after the jet landed.

"How could you lose a passenger?" Watts, who did not fly with her husband that day, told The Indianapolis Star. "If I was somewhere on that plane, I would hope someone would notice."

Tim Smith, a spokesman for American Airlines in Fort Worth, Texas, said the company does not comment on pending litigation.