Fort Hood, Texas (CNN) -- The suspect in last week's deadly shooting spree at Fort Hood urged in 2007 that Muslims in the U.S. Army be allowed to claim conscientious objector status when it comes to fighting other Muslims in war, a defense official said Tuesday.

Maj. Nidal Malik Hasan also discussed religious aspects of Islam during a presentation at Walter Reed Army Medical Center as part of a final project for his residency tenure, said the official, who has knowledge of the investigation into Hasan.

"It's getting harder and harder for Muslims in the service to morally justify being in a military that seems constantly engaged against fellow Muslims," Hasan said, according to a slide show that The Washington Post said Hasan used in the June 2007 presentation.

"Muslims [sic] soldiers should not serve in any capacity that renders them at risk to hurting/killing believers unjustly," a Hasan slide said, though he added that individual feelings "will vary!"

Hasan is the only suspect in the shooting at the Fort Hood Army post in Texas on Thursday that left 13 people dead and 42 wounded. Twelve of the dead were soldiers.

Hasan remains in intensive care at Brooke Army Medical Center in San Antonio, Texas, after having been shot by a police officer.

Dr. Val Finnell, a former medical school classmate of Hasan's, described him as "a very outspoken opponent of the war" in the classroom and in public settings.

"He equated the war against terror with a war against Islam," Finnell said.

He added that he was shocked by Thursday's shooting.

"However, that said, given the things that Maj. Hasan has said to me in the past and to other people, I am not surprised."

Hasan's comments came in what was supposed to be a medical seminar, The Washington Post reported, but instead he spoke to senior Army doctors about Islam.

Hasan, a psychiatrist, aimed to describe "religious conflicts that Muslims may have with the current wars in Iraq and Afghanistan," according to the newspaper's report.

The report is based on a slideshow that The Washington Post said Hasan used in the June 2007 presentation.

See the presentation and the Post's report

In a statement issued Monday night, the FBI said its investigation "indicates that the alleged gunman acted alone and was not part of a broader terrorist plot."

Hasan came under investigation for a time last year when his communications with radical cleric Anwar al-Awlaki were intercepted by terrorism investigators monitoring the cleric's communications, a federal law enforcement official said.

An employee of the Defense Department's Criminal Investigative Services, assigned to the Joint Terrorism Task Force, ultimately made the decision to drop the investigation after reviewing the intercepted communications and Hasan's personnel files.

However, a senior defense department official said late Tuesday that the agency was not aware of any such communication.

"Contrary to reports we have seen in some news outlets, based on what we know now, neither the United States Army nor any other organization within the Department of Defense knew of Major Hasan's contacts with any Muslim extremists," the official said. "Not until after the tragic shooting at Fort Hood last week were Major Hasan's e-mail communications first brought to our attention by federal investigators."

President Obama traveled to Fort Hood for a memorial service on Tuesday for the victims of the shooting. Defense Secretary Robert Gates, Texas Gov. Rick Perry and other dignitaries also attended the service.

Read profiles of the shooting victims

Hasan, 39, was wounded several times during the attack. His ventilator was removed over the weekend, and he began talking afterward, hospital spokesman Dewey Mitchell said.

Federal agents attempted to interview Hasan on Sunday, but he refused to cooperate and asked for an attorney, according to senior investigative officials, who insisted they not be identified by name because of the sensitive nature of the ongoing federal investigation.

Hasan has retained a lawyer, ex-military judge and retired Army Col. John Galligan, the attorney told CNN affiliate KXXV-TV.

"Like anybody that's facing criminal charges in the military arena, he's entitled to a defense counsel," Galligan told the station.

Galligan said he had a 25-minute conversation with Hasan, and the two did not talk much about the Fort Hood shooting.

"There's still a lot to be done on the medical side," Galligan said.

Hasan, a U.S.-born citizen of Palestinian descent, was a licensed psychiatrist who joined the Army in 1997. He was promoted to major in May and was scheduled to deploy to Afghanistan sometime soon but had been telling his family since 2001 that he wanted to get out of the military.

Hasan, a Muslim, also told his family that he had been taunted after the terrorist attacks of September 11. In August, he reported to police that his car was keyed and a bumper sticker that read "Allah is Love" was torn off. A neighbor was charged with criminal mischief after that complaint.