Former Marine reservist pleads guilty in Pentagon shooting incident January 26, 2012 -- Updated 1721 GMT (0121 HKT) Yonathan Melaku pleads guilty to charges including injury to U.S. property He was accused of shooting at the Pentagon and other military-related buildings He is sentenced to 25 years in prison Alexandria, Virginia (CNN) -- A 23-year-old former Marine Corps reservist accused of shooting at the Pentagon and other military-related buildings in late 2010 pleaded guilty to three counts on Thursday. Yonathan Melaku agreed to a 25-year prison sentence. If he had been convicted on all the federal charges, he would have faced a maximum life sentence. Melaku pleaded guilty to injury to property of the United States by shooting with a firearm; using, carrying and discharging a firearm during a crime of violence; and attempted injury to veterans' memorials. Melaku attempted to flee law enforcement officers in June 2011 when they found him trespassing in Arlington National Cemetery, but he was apprehended. He discarded a backpack in which police found 9 mm casings, numerous Arabic statements referencing al Qaeda, and plastic bags containing ammonium nitrate, according to a police affidavit. It was disclosed Thursday that Melaku's intention was to spray-paint grave markers with Arabic statements.