The State Department investigation of improper computer access to passport records of three presidential candidates is focusing on one remaining employee — a contract worker with a company headed by an adviser to the presidential campaign of Sen. Barack Obama

The third employee, who has not been fired, worked for The Analysis Corporation (TAC), which is headed by John O. Brennan, a former CIA agent who is an adviser to Mr. Obama's presidential campaign on intelligence and foreign policy.

The TAC employee is the only individual to have accessed both Mr. Obama's and Mr. McCain's passport information without proper authorization, a State Department spokesman said. That employee, who was not named, triggered an electronic alarm system, officials familiar with the probe said.

The accessed records have the data provided in passport applications and used by the department to issue or renew travel documents.