MADISON – Federal prosecutors have identified two former guards as targets of an excessive force probe at the state’s Northwoods juvenile prison, according to sources and one of the targets.

U.S. Attorney Scott Blader’s office informed the two guards in writing that they were targets of the wide-ranging investigation into activities at Lincoln Hills School for Boys north of Wausau.

The letters are the first concrete sign prosecutors are moving toward charges with an investigation that began nearly three years ago. A grand jury is scheduled to take up the case Wednesday behind closed doors.

“I did absolutely nothing wrong. I did my job,” one of the targets said in a brief interview Saturday.

The Milwaukee Journal Sentinel is not naming the targets because they have not been indicted and do not appear to have retained lawyers yet.

At issue is a 2014 incident in which a teen prisoner’s arm was injured after guards bent back the inmate's wrist and brought him to his knees. Local officials declined to issue charges at the time of the incident, but federal prosecutors are now revisiting it.

State Attorney General Brad Schimel began the probe in January 2015 and turned it over to federal prosecutors and the FBI a year later. Investigators are looking into allegations of prisoner abuse, child neglect, tampering with public records and other potential crimes.

Separately, several lawsuits have been filed over the institution, including one that resulted in an injunction this summer forcing the state to limit the use of solitary confinement and pepper spray.

A Journal Sentinel review last year found widespread problems at Lincoln Hills and its sister facility, Copper Lake School for Girls, which sits on the same grounds. Interviews and more than 1,000 pages of records showed guards were trained improperly, supervisors failed to preserve video evidence and institution leaders often didn’t notify parents or law enforcement when teen inmates were injured.

State Department of Corrections officials have emphasized changes they have made in recent years, including greatly expanding staff training and equipping workers with body cameras.

The target letters focus on a March 2014 incident that began when a teen inmate blocked the camera and window to his cell door, preventing guards from seeing inside, according to prison documents released to the Journal Sentinel last year under the state’s open records law. The inmate threatened to use a large screw to injure himself or staff, according to those records.

The two guards who recently received target letters secured the inmate’s arms. One of them bent the inmate’s wrist back and brought him to his knees, according to the records. The two guards performed a strip search while another guard searched the room, but no one found a screw.

Afterward, the inmate reported his arm hurt. It is unclear how serious the injury was or how soon he saw a nurse or doctor because the state blacked out parts of the report to keep medical information private.

No one documented the incident when it happened. Seven days later, the prison’s security director at the time, Bruce Sunde, told staff to write reports because the inmate was alleging excessive force had been used. Workers wrote those reports over the following two days.

The Lincoln County Sheriff’s Office was notified of the incident a week after it occurred. The Lincoln County district attorney declined to prosecute, the state records show.

Sunde and other prison officials conducted a use-of-force review two weeks after the incident occurred. They labeled the incident “unremarkable.”

An internal investigator reviewed the incident again in 2015. She found one of the former guards who recently received a target letter had violated department policy because the strip search of the inmate had not been documented, but she did not find fault with other aspects of how he handled the incident.

The other guard retired in December 2015, while he was under an internal investigation. It was not clear if that investigation was related to the March 2014 incident or another one.

The Journal Sentinel was unable to find contact information for that former guard.

The other one acknowledged he'd received the target letter and said he didn't plan to go to the grand jury. He said he could not remember how seriously the inmate might have been injured or other aspects of the incident.

"I have no idea what this is about and I have no worries about anything," he said.

The letters were sent a month after Blader was sworn in as U.S. attorney and assumed control of the investigation. Blader and an aide did not respond to questions on Saturday.