The Pennsylvania man accused of fatally shooting and subsequently beheading his father before posting it on YouTube testified on Wednesday that the killing was his “Plan B” after attempting to arrest his father for what he described as false statements and treason.

Justin D. Mohn, 33, provided testimony in a suburban Philadelphia courtroom on the third day of his trial, facing murder and additional charges related to the homicide of his father, Michael F. Mohn, which occurred on January 30, 2024.

Mohn, dressed in a blue sport coat, shirt, and tie, with his hands shackled to his waist, spoke clearly and without any noticeable emotion during over two hours of direct testimony and cross-examination.

Responding to questions from his attorney, Steven Jones, Mohn said he shot his father in the bathroom of the family’s Levittown home after telling him he was going to arrest him. Mohn said his father, who he said was an experienced martial artist, told him he would kill him before he let that happen and reached for the gun.

“Unfortunately, he resisted,” Justin Mohn said, adding: “I was hoping to perform a citizen’s arrest on my father for, ultimately, treason.”

He described a list from his notebook, shown during the trial, that had the lines “Boom” and “Slice” as his “Plan B,” and said he expected his father to go along with the citizen’s arrest.

He said he differed politically from his parents, describing them as on the left. He told the court he believed his father wanted to stop him from becoming a politician similar to President Donald Trump and that his father gave false statements in an unrelated civil case Justin Mohn brought in federal court.

Asked why he beheaded his father, he said he wanted to send a message to federal government workers to meet his demands, which included their resignation as well as the cancellation of public debt, among other things. He said he didn’t do it out of hatred for his father or to cause trauma to his family. His mother, Denice Mohn, cried in court at the end of the direct questioning from his attorney.

“I knew something such as a severed head would not only go viral but could lessen the violence,” Justin Mohn said.

Prosecutors said Mohn shot his father with a newly purchased pistol, then decapitated him with a kitchen knife and machete. The 14-minute YouTube video he posted was live for several hours before it was removed.

Mohn was arrested later that day after scaling a fence at Fort Indiantown Gap, the state’s National Guard headquarters. He said in court he knew it was wrong to jump the fence at the site. Prosecutors said he called for others to join him in attempting to overthrow the U.S. government.

Mohn had a USB device containing photos of federal buildings and apparent instructions for making explosives when he was arrested, authorities said.

He also expressed violent anti-government rhetoric in writings he published online, going back several years. Earlier in the trial, the judge heard from Justin Mohn’s mother, who said police came to the house he shared with his parents and warned him about his online postings before the killing.

Every morning, the NY POSTcast offers a deep dive into the headlines with the Post’s signature mix of politics, business, pop culture, true crime and everything in between. Subscribe here!

Denice Mohn testified that she and her husband had been offering financial support and guidance as Justin Mohn looked for a job.

Prosecutors described the homicide as “something straight out of a horror film.” They said Justin Mohn killed his father — who had been an engineer with the geoenvironmental section of the U.S. Army Corps of Engineers’ Philadelphia District — to intimidate federal workers, calling it a “cold, calculated, organized plan.”

The YouTube video included rants about the government, immigration and the border, fiscal policy, urban crime and the war in Ukraine.

In court, Michael Mohn was remembered as a good neighbor and supportive father. In the video posted on YouTube, Justin Mohn described his father as a 20-year federal employee and called him a traitor.

During a competency hearing last year, a defense expert said Mohn wrote a letter to Russia’s ambassador to the United States seeking to strike a deal to give Mohn refuge and apologizing to President Vladimir Putin for claiming to be the czar of Russia. The judge ruled Mohn was competent to stand trial.

Evidence presented at the trial included graphic photos and the video posted to YouTube. The judge warned members of the public at the trial about the images and said they could leave before the photos were shown. The proceedings are known as a bench trial, with only a judge, not a jury.