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A photograph showing a group of men with guns posing with a bullet-riddled T-shirt containing an image of Barack Obama's face is to be investigated by the Secret Service, a spokesman confirmed to NBC News.

The New York Times reported that the picture showed seven young men, four with weapons, one of whom was holding a T-shirt with the president's face on it, above the word "HOPE." The T-shirt was covered in holes and gashes.

The Times said the photograph was posted on the Facebook page of a Peoria, Ariz., police officer, Sgt. Pat Shearer, on Jan. 20.

"We are aware of it. Anytime information is brought to our attention that a group or individual expresses an unusual interest in one of our protectees, we conduct the appropriate follow-up," Secret Service spokesman Max Milien told NBC News.

"We respect the right of free speech and expression but we certainly have the right and obligation to speak to individuals to determine what their intent is," he added. "We treat anything (any potential threat) seriously. We can't dismiss anything."

'Administrative investigation'
Jay A. Davies, a police spokesman, told the Times in an email that "an administrative investigation into any possible policy violations on the part of our employee" was being carried out.

The paper added that the photograph also appeared on the Facebook page of someone in the picture, who was identified as a Peoria high school student.

Shearer, who said he would sacrifice his life for President Barack Obama, told ABC15 that he didn't "think that them shooting up the T-shirt was a big deal."

"I think it was more of a political statement obviously," he added. "It’s not like they were going to go out and shoot the president.”

Assassination charges
The incident follows the case of an Idaho man accused of firing shots at the White House. On Tuesday, he pleaded not guilty to charges that he tried to assassinate President Barack Obama.

A lawyer for Oscar Ramiro Ortega-Hernandez entered the plea on his client's behalf during a brief appearance in U.S. District Court in Washington.

Ortega did not say anything during the proceedings and will remain held without bond. He has another court date next month.

Gunman who shot at federal buildings pleads guilty

Prosecutors say Ortega used an assault rifle with an attached scope to fire a series of shots at the White House from long range on the night of Nov. 11. Obama and his wife, Michelle, were out of town at the time.

In the months before the shooting, investigators say, he had had become obsessed with Obama, referred to him as the anti-Christ and told at least one person that he planned to "take care of" the president.

Obama turns attention to energy in key states

Ortega, of Idaho Falls, Idaho, was indicted last week on 17 counts including trying to assassinate the president, transporting a firearm across state lines and assaulting officers or employees of the United States with a deadly weapon.

Those charges refer to three Secret Service employees who authorities say were on the grounds of the White House at the time of the shooting.

The hearing took place in the same week that a lawyer for John Hinckley, who was found not guilty by reason of insanity in a 1981 assassination attempt on President Ronald Reagan, is making his case for extended time away from the psychiatric hospital where Hinckley has been confined.

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NBC News and The Associated Press contributed to this report.