Sheriff allegedly shoots judge in his office

After a Kentucky sheriff was arrested for allegedly shooting a judge in his office, investigators are searching for a motive, officials said.

Letcher County Sheriff Shawn Stines has been charged with first-degree murder for allegedly shooting Kentucky District Judge Kevin Mullins at the Letcher County Courthouse Thursday afternoon, officials said.

A 911 caller reported gunshots in the courthouse and emergency responders found 54-year-old Mullins with multiple gunshot wounds, Kentucky State Police said. He was shot in his office, said Kentucky Governor Andy Beshear.

Stines, 43, allegedly shot Mullins “after an argument inside the courthouse,” Kentucky State Police said. Officials said they had not yet determined whether Stines used his “service weapon.”

He was taken into custody at the courthouse without incident.

Stines is cooperating with authorities conducting the investigation, officials said. It was unclear whether Stines has an attorney.

The motive is still under investigation, Kentucky State Police Detective Matt Gayheart told ABC affiliate station WJHL in Johnson City, Tennessee.

No one else was in the judge's chambers at the time of the shooting, Gayheart said.

“This is an isolated case and there is no danger to the public,” he said.

Kentucky Attorney General Russell Coleman said his office will work with 27th Judicial District Attorney Jackie Steele as special prosecutor in the case.

According to an order from Letcher County Judge and Chief Administrative Officer Terry Adams, the courthouse will be closed Friday.

Letcher County District Attorney Matt Butler has recused himself from the case.

Butler not only worked with the sheriff but also had a “close, personal relationship” with the judge, he announced in a self-recorded video on Friday.

Butler and Mullins were formerly brothers-in-law when they were married to two sisters, Butler said.

“His daughters are my nieces. My two oldest children are his niece and nephew,” Butler said. “As a brother-in-law, I will never forget how kind he was to my children.”

And when the judge was the prosecutor and Butler was the public defender, they faced each other in court but always remained friendly outside of court, Butler said.

In his message, Butler urged people to “pray for everyone involved.”

Laurance B. VanMeter, chief justice of the Kentucky Supreme Court, said in a statement that he was “shocked by this act of violence,” adding that the “court system is shaken by this news.”

“My prayers are with his family and the Letcher County community as they try to process and mourn this tragic loss. On their behalf, I ask for respect and privacy,” he said.

“While the investigation is ongoing, we are committed to assisting in any way we can,” the Kentucky Court of Justice said in a statement. “Our deepest sympathies go out to all those affected by this tragic event, and our thoughts and prayers are with the community during this difficult time.”

Mullins had been a district judge in Kentucky's 47th District Court, which covers Letcher County, since 2009. At that time, he was appointed by then-Governor Steve Beshear, the current governor's father.

He graduated from the University of Kentucky and received his law degree from the University of Louisville.

Letcher County is located on the border between Kentucky and Virginia, about 150 miles southeast of Lexington, Kentucky.

ABC News' Victoria Arancio, Jack Date, Darren Reynolds and Leah Sarnoff contributed to this report.