An FBI financial analyst from Dallas and her son pleaded not guilty Thursday to charges that they committed wire fraud and tax evasion for falsifying paperwork on several high-dollar vehicle loans.

The bureau placed Deborah Lee Stinson, 55, a 20-year FBI support employee, on administrative leave earlier this year after the allegations surfaced, officials said. She and her son, Mark Alan Stinson, 27, also of Dallas, turned themselves in Thursday after they were indicted the previous day.

Prosecutors say that last year, Ms. Stinson was given large amounts of cash by her son that she used to obtain loans for more than a quarter-million dollars' worth of vehicles. She falsely claimed they were hers, authorities allege.

The vehicles, all 2007 models, included a Mercedes E350, a Mercedes S550, a Cadillac Escalade and a Honda racing motorcycle.

Authorities did not comment on where Mr. Stinson got the tens of thousands of dollars used in the alleged straw purchases, but said that no FBI money was involved and no cases were compromised.

Mr. Stinson was cleared by a Dallas County grand jury in the Aug. 1 death of 24-year-old Mario Moreland. Mr. Moreland was with a group of home invaders that broke into Mr. Stinson's northeast Dallas home last year. Mr. Stinson shot at the intruders as they left, and Mr. Moreland died.

Dallas police detectives found several guns inside Mr. Stinson's home and also noticed several luxury vehicles there registered to Mr. Stinson's mother, who they found worked for the FBI.