Federal prosecutors are trying to determine if a Wal-Mart systems technician who was fired for spying on fellow employees broke any federal laws.

Wal-Mart said last week that the employee was fired for intercepting text messages and recording telephone conversations without authorization. The company conducted an internal investigation that started after one of the employee's colleagues "expressed concerns" about the recordings, according to a release from Wal-Mart.

Now the U.S. Attorney's Office in the Western District of Arkansas is investigating, says First Assistant U.S. Attorney Deborah Groom.

The technician had monitored and recorded telephone conversations between Wal-Mart public relations associates and a reporter from The New York Times, Wal-Mart said. The recordings were made over a four-month period between September 2006 and January. Wal-Mart said it has taken steps "to strengthen our policies and controls" to prevent such spying.

Wal-Mart's initial assessment was that the employee violated company policies but hadn't broken any laws, though it reported the matter to the U.S. attorney. What remains unclear is why the employee was intercepting messages and recording phone conversations, and why it went on so long.