The FBI used a variety of informal methods that circumvented the law to obtain thousands of phone call records for terrorism investigations, the Justice Department's inspector general said in a report Wednesday.

The 289-page examination said that for several years the FBI obtained some phone records through requests by e-mail, post-it notes, by telephone and by what the FBI referred to as "sneak peeks" — all informal approaches that the inspector general found were improper.

The FBI's Communications Analysis Unit made informal requests for the call records associated with at least 3,500 telephone numbers. The IG said it could not determine the full scope of the practice because of the FBI's inadequate record-keeping.

Regarding the use of "sneak peeks," employees of phone companies would check their records and provide the FBI with a preview of the available information for a targeted phone number, without any written justification for the request from the FBI, and often without documentation that such a request had even been made.

Part of the IG's examination focused on the use of 700 exigent letters to obtain the calling records for more than 2,000 phone numbers from 2003 to 2006. The IG concluded that contrary to the statements in the letters, many of the investigations for which the letters were used did not meet legal standards.

The FBI's practices are "troubling" and the bureau and the Justice Department need to take steps to ensure that agents obtain records in accord with the law and department policies, Inspector General Glenn Fine said in a statement.