Boston (WBZ Newsroom)  -- The controversy surrounding bodybuilder firefighter Albert Arroyo shows no sign of abating.

Sources tell WBZ's Lisa Meyer that the state medical registration board has begun an investigation of Dr John Mahoney, the doctor who certified Arroyo as disabled.

A watchdog group says the incident has dealt the already tarnished image of the Boston Fire Department yet another damaging blow.

For the record, the medical board won't comment on whether Mahoney is being investigated, saying that information is confidential.

Sources say the probe began this week. In the last seven years, Mahoney has treated 25 firefighters seeking tax free disability pensions, 21 cases were okayed and four more are in the pipeline. Mahoney didn't return our calls and neither did Arroyo's lawyer or firefighters union chief Ed Kelley.

Sam Tyler at the Boston Municipal Research Bureau says couple this with the ongoing federal criminal investigation into the fire department and it's not exactly the best public relations you could get. He tells WBZ Newsradio 1030 indictments might actually help clean things up.