9 News has learned the fire marshals office in Arlington is digging into the background of one of its own veteran fire investigators and inspectors.

9 News has learned that a local fire marshal is under investigation after questions are raised about his qualifications.

With arson very much in the news, the Arlington County probe has the potential to damage arson cases that this investigator has handled.

Dave Statter has our exclusive story

At a recent house fire in Arlington, County fire marshals were digging for clues. 9 News has learned the fire marshals office is also digging into the background of one of its own veteran fire investigators and inspectors.

For almost 14 years, firefighter Thomas F. Cooper has been assigned to the Arlington Fire Marshals office.

But it was only three months ago when Cooper's bosses began to question Cooper's qualifications that allow him to inspect County buildings for fire code and life safety violations.

Sources familiar with the probe say the investigation is specifically looking at Cooper's state credentials and the validity of those credentials.

In Arlington County Fire Marshals perform both inspections of buildings and investigate fires. Sources say while Cooper?s qualifications as a fire investigator have not been called into question, there is a potential problem with any arson cases Cooper has been involved in.

Sources say the Arlington County Fire Department has notified the Commonwealths Attorney, and the U.S. Attorney of the investigation. The reason, the probe could allow a defense attorney to challenge Cooper's credibility as a witness.

It is unclear how many cases that could effect. The look at credentials in the Fire Marshal's office began in September shortly after chief James Schwartz took over the department.

Today he said by phone "When we learned of the issue we took immediate steps to remove firefighter Cooper from his position as fire inspector and investigator. We immediately undertook an investigation to ascertain the validity of his certifications. We regret that a records check didn't call into question the verification of the certification earlier."

The probe into firefighter cooper is expected to wrap up soon. If the allegations are sustained there is the potential for Cooper to lose his job. Cooper also received premium pay for many years because of his qualifications. Reached at home today firefighter Cooper told us he would have no comment.

Click on video to see Dave Statter's report.