Attorney General Investigating DiPaola

A complaint against Middlesex County Sheriff James DiPaola has been referred to the attorney general's office for investigation.

Allegations of improper campaign donations were included in the complaint, which the Middlesex District Attorney's office received last Thursday, according to office spokeswoman Jessica Venezia-Pastore.

The information was referred to Attorney General Martha Coakley's office days later, Venezia-Pastore said. She refused to comment on the source of the complaint, and referred further questions to the attorney general's office.

Coakley's office received the complaint on Monday and it is under review, Deputy Press Secretary Harry Pierre said Wednesday. He refused further comment on the matter.

The complaint came amid allegations that DiPaola planned to exploit a pension loophole to collect nearly $100,000 annually on top of his salary.

Though re-elected to his third term as Sheriff weeks earlier, DiPaola abruptly announced his retirement in advance of a Boston Globe investigation published on Sunday.

The Globe Spotlight Team report said the former Malden police officer was not planning to do anything illegal but intended to exploit a loophole in the regulations that would have allowed him to collect a $98,500 annual pension on top of his $123,000 sheriff's salary.

In a letter to Middlesex Country residents, DiPaola said he would work without salary until January 2011 to give Governor Deval Patrick time to announce a replacement.

"I made a black and white decision based on finances instead of my moral compass to run for re-election and to apply for retirement," said DiPaola in the letter.