A defense manufacturer is suing ABC News to regain what the company said were stolen documents used for a story on reputed parts overcharges for a U.S. Army vehicle. ``We don't know how they got the documents,'' said Pat Brozowski, spokeswomen for FMC Corp., the Chicago-based builder of the Bradley Fighting Vehicle. The ABC World News Tonight segment, which aired Oct. 20 quoting unidentified former FMC employees, accused the company of overcharging the government for spare parts on the vehicle, which resembles a tank. ``We have not seen the lawsuit and cannot comment at this time,'' spokeswoman Elise Adde of ABC News said from New York. An in-house investigation of the television story ``turned up the fact that the documents were missing from our files,'' Ms. Brozowski said. The lawsuit was filed Wednesday in Cook County Circuit Court. FMC also said it has told the government's General Accounting Office it will cooperate with any investigation of prices charged on the Bradley parts, according to the statement.