KILLEEN, TX --An AWOL infantry soldier caught with weapons and a bomb inside a backpack admitted planning what would have been Fort Hood's second terrorist attack in less than two years, the Army said Thursday. He might have succeeded at carrying it out, police said, if a gun-store clerk hadn't alerted them to the man's suspicious activity. "We would probably be here today, giving you a different briefing, had he not been stopped," Killeen Police Chief Dennis Baldwin said. The 21-year-old suspect, Pfc. Naser Abdo, was arrested Wednesday at a motel about three miles from Fort Hood's main gate. He had spoken out against the 2009 Fort Hood shootings last year as he made a public plea to be granted conscientious objector status to avoid serving in Iraq or Afghanistan. Like the soldier charged with killing 13 people in the shootings, Abdo is Muslim, but he said in an essay obtained by The Associated Press the attacks ran against his beliefs and were "an act of aggression by a man and not by Islam." Abdo was approved as a conscientious objector this year, but that status was put on hold after he was charged with possessing child pornography. He went absent without leave from Fort Campbell, Ky., during the July 4 weekend. On July 3, he tried to purchase a gun at a store near the Kentucky post, according to the company that owns the store. Abdo told an AP reporter a week later that he was concerned about his safety and had considered purchasing a gun for protection, but had not yet done so. Police in Killeen said their break in the case came from Guns Galore LLC -- the same gun store where Maj. Nidal Hasan bought a pistol used in the 2009 attack. Store clerk Greg Ebert said the man arrived by taxi Tuesday and bought 6 pounds of smokeless gunpowder, three boxes of shotgun ammunition and a magazine for a semi-automatic pistol. Ebert said he called authorities because he and his co-workers "felt uncomfortable with his overall demeanor and the fact he didn't know what the hell he was buying." According to an Army alert sent via email and obtained by The Associated Press, Killeen police learned from the taxi company that Abdo had been picked up from a local motel and had also visited an Army surplus store where he paid cash for a uniform bearing Fort Hood unit patches. Agents found firearms and "items that could be identified as bomb-making components, including gunpowder," in Abdo's motel room, FBI spokesman Erik Vasys said. The Army alert said Abdo "was in possession of a large quantity of ammunition, weapons and a bomb inside a backpack," and upon questioning admitted planning an attack on Fort Hood. Officials have not offered details about a possible motive. Baldwin, the police chief, said Abdo "was taken down rather quickly without incident." Vasys said the FBI would charge Abdo with possessing bomb-making components and he would be transferred from Killeen police into federal custody. Vasys said there was nothing to indicate Abdo was working with others. An Oklahoma attorney who has represented Abdo said Thursday he hadn't heard from Abdo in weeks. "I've been quite anxious to get in touch with him," said attorney James Branum. The AP was among the media outlets to interview Abdo in the past year when reporting on his request for objector status. On Tuesday, July 12, Abdo contacted an AP reporter with whom he had spoken previously, said he had gone AWOL and considered purchasing a gun for personal protection. Abdo said he had not yet done so, because he knew he would have to give his name and other information to the gun dealer. Abdo said he had received critical emails about his conscientious objector case and was worried about his safety as an increasing number of soldiers were returning to Fort Campbell from Afghanistan. The AP described the contents of this conversation that Thursday to a civilian Army spokesman. The next day, when contacted by Army investigators, the AP said it did not know Abdo's location and provided the telephone number from which he made his original call. An Article 32 military hearing last month had recommended that Abdo be court-martialed over military charges that 34 images of child pornography were found on a computer he used. In addition, the military's criminal investigation division, along with the federal Joint Terrorism Task Force, investigated Abdo earlier after he was flagged for making unspecified anti-American comments while taking a language class, according to a U.S. official briefed on the investigation. The official, who spoke on condition of anonymity because the investigation is ongoing, said neither the military nor the task force discovered anything at the time to indicate Abdo was planning an attack, the official said. FBI, police and military officials have said little about whether or how they were tracking Abdo since he left Fort Campbell. Patrick J. Connor, special agent in charge with Army Criminal Investigation Command at Fort Hood, said efforts had been made to locate him after an arrest warrant was issued but he would not elaborate. Abdo grew up in Garland, a Dallas suburb about 170 miles from Fort Hood. In his essay, which he sent to the AP last year as he made his conscientious-objector plea, he said his mother is Christian and his father is Muslim, and that he decided to follow Islam when he was 17. "Little did I know that when I first became a Muslim that I was going to learn what Islam meant to me and what I was willing to sacrifice for it," he wrote. He wrote that he joined the Army believing he could serve in the military and honor his religion, but he ended up having to endure insults and threats from fellow soldiers over his religion during basic and advanced training. He said life was better after he arrived at his first duty station, but that he studied Islam more closely as he neared deployment to learn "whether going to war was the right thing to do Islamically." "I began to understand and believe that only God can give legitimacy to war and not humankind," he wrote. "That's when I realized my conscience would not allow me to deploy." His application was filed in June 2010. The Army's Conscientious Objector Review board denied his request, but the deputy assistant secretary of the Army Review Boards Agency recommended he be separated from the Army as a conscientious objector. The discharge was delayed when he was charged with possession of child pornography on May 13. Fort Campbell civilian spokesman Bob Jenkins said Abdo had been aware of the child pornography investigation since November. Abdo lived for about five years with his mother and sister in a corner duplex in Garland, according to a neighbor, Yawonna Wilson. Wilson said the family moved out about a year ago. Shakira Doss, a neighbor who went to the same Dallas-area high school as Abdo and was good friends with his sister, said she wasn't surprised by news of the alleged plot because the suspect seemed "weird." When she visited Abdo's duplex, Doss said he would spend most of the time in his room. Abdo's sister "had all the friends," said Doss, a 17-year-old high school senior. "Her brother just didn't fit in." Abdo attempted to purchase a gun July 3 from Quantico Tactical, a store near Fort Campbell in Oak Grove, Ky., said David Hensley, president of the seven-store chain. Hensley said Abdo went into the store twice that day. The first time, after asking questions, he left. The second time, he attempted to buy a handgun, Hensley said. "He exhibited behavior that alerted our staff and our staff refused to, based upon that behavior, sell him a firearm," he said. Hensley said normally when someone buys a weapon, federal paperwork is filled out and there is an instant background check by the FBI, but the attempted purchase didn't get to that stage.