State Attorney General Maura Healey's office is convening a grand jury as part of the investigation into alleged theft of overtime money by members of the Massachusetts State Police, sources told MassLive.

Healey's office declined to comment about the grand jury. A spokeswoman for Healey said the investigation remains active and ongoing.

The investigation by Healey's office is separate from the continuing federal investigation that has led to six troopers facing charges in U.S. District Court. No trooper has been charged on a state level in connection with the overtime investigation as of Aug. 31.

A total of 46 Massachusetts State Police troopers are under investigation for allegedly stealing overtime pay while claiming to conduct specialized traffic enforcement on the Massachusetts Turnpike and Metropolitan tunnels system.

The specialized patrols, known as Accident Injury Reduction Effort patrols, and X-Team patrols, are at the center of the investigation. State police audited the patrols for 2016 and discovered discrepancies between overtime pay and hours worked.

The audits expanded into 2015 AIRE and X-Team patrols and other patrols conducted by Troop E.

The six troopers facing federal charges are all accused of embezzling money from an agency receiving federal funds. Sources did not know what possible charges Healey is pursuing in the state's investigation into the alleged overtime theft.

Two of the six troopers have pleaded guilty in the federal case.

Federal investigators accuse the troopers charged in U.S. District Court of skipping the overtime shifts or working partial shifts. FBI agents reviewed data from the troopers' cruisers to follow their locations.

Investigators also say they discovered troopers wrote phony citations or changed dates on previously written citations, so the troopers could appear to be working the specialized shifts, federal court records say.

One of the two troopers who pleaded guilty in federal court, Trooper Gregory Raftery, skipped or partially worked 116 AIRE shifts, MassLive learned.

MassLive Reporter Gintautas Dumcius contributed to this report