Boston Police Officer John O'Keefe was found unresponsive in January 2022 outside this residence in Canton, Massachusetts.
CNN  — 

A state trooper investigating the death of a Boston police officer is now under investigation himself, authorities said Thursday, adding another layer of complexity to a case that has sharply divided a Massachusetts suburb.

The Massachusetts State Police said it has opened an internal investigation into a “potential violation of department policy” against Trooper Michael Proctor, one of the lead investigators in the death of Officer John O’Keefe. It did not elaborate on what he is being investigated for.

Investigators allege O’Keefe’s girlfriend, Karen Read, hit him with her SUV in the Boston suburb of Canton in January 2022 and left him outside in the snow to die.

But Read’s defense team alleges that he was fatally beaten in the Canton home of a fellow Boston police officer, and that Read is the victim of a coverup to protect those inside the home that night. Read has said she dropped O’Keefe outside the home shortly after midnight  — after they left a bar — then drove off to his house to sleep because she was not feeling well.

O’Keefe’s body was found about six hours later outside the home. Read has pleaded not guilty to second-degree murder, vehicular manslaughter while intoxicated and leaving the scene of a collision.

The Massachusetts State Police did not specify whether Proctor’s alleged violation is related to Read’s case. “Trooper Proctor remains on full duty,” a State Police spokesperson said in a statement to CNN on Thursday.

This undated photograph provided by the Boston Police Department shows officer John O'Keefe, 46, of Canton, Mass. O'Keefe died at an area hospital after being found lying in snow unresponsive outside his home on Saturday Jan. 30, 2022. Karen Read, 41, of Mansfield, Mass., was charged with manslaughter on Wednesday Feb. 2, 2022 after allegedly striking O'Keefe, her boyfriend, with her car. Read pleaded not guilty to manslaughter and other charges at her arraignment Wednesday. (Boston Police Department via AP)

“Please note that we are not stating whether the potential violation relates to a specific case, nor are we specifying the nature of the alleged violation.”

David Traub, a spokesperson for the Norfolk District Attorney’s Office, which is prosecuting Read’s case, told CNN they’re aware of the investigation. Proctor remains “on full duty and his responsibilities within our office have not changed,” he said.

The investigation comes the same week Read’s defense team alleged that Proctor did not fully disclose his relationship with key witnesses in the case. During a hearing Tuesday, attorney Alan Jackson alleged that text messages revealed Proctor has close ties with the family of the homeowner, and has communicated with them before and after O’Keefe’s death.

“We’ve been saying since September 2022 motions that we filed before this court and filed with the Commonwealth that there is a conflict. You’re not investigating the conflict. That conflict was never described to the grand jurors. And we’ve been rebuffed at every single turn,” Jackson said in court on Tuesday.

Karen Read is shown with her defense attorneys, Alan Jackson, (left) and David Yannetti at Norfolk County Superior Court.

Proctor’s attorney, Michael DiStefano, said his client is cooperating with the investigation.

“Trooper Proctor remains steadfast in the integrity of the work he performed investigating the death of Mr. John O’Keefe,” he said in a statement obtained by CNN. “To the extent that Trooper Proctor’s personal text messages are alluded to in court proceedings regarding Ms. Read, he respectfully submits that the objective investigative steps he and members of his unit took are in no way undermined by the content of the personal messages.”

Norfolk County Assistant District Attorney Adam Lally has said the defense is using the relationships to distract from Read’s alleged guilt, CNN affiliate WFXT reported.

“It’s a three-card Monte trick. You know, card trick. On the corner, on the side. Look at all of this. Look at this relationship. Look at that relationship,” Lally said.

Read’s trial is scheduled to start next month.