Concerns about political correctness tainted the FBI's investigation of Army Major Nidal Hasan in the months before he gunned down dozens of people at Fort Hood in November 2009, the chairman of a House subcommittee investigating the massacre said during a hearing Wednesday.

The failures by the FBI and Army to follow warning signs properly for nearly a year contributed to "a bunch of dead people stacked up at Fort Hood," said Rep. John Carter, the Texas Republican who represents the area, in one of many heated exchanges with a top bureau official.

‘I am concerned that there were warning signs, and that with more aggressive investigation, there is a chance that this incident could have been prevented. - Rep. Frank Wolf, R-VA’

Hasan came to the FBI's attention in December 2008, nearly a year before be opened fire at the Army base, killing 13 and wounding 42, according to an investigative report on the bureau's conduct by former agency director William Webster that was released last month.

The Army psychiatrist sent an email to radical Imam Anwar al-Aulaqi, an American-born cleric who later became the chief propagandist for al-Qaeda and was killed last September in a U.S. drone strike in Yemen.

By the time of the shooting in November 2009, Hasan had sent Aulaqi more than a dozen additional emails on topics ranging from the mundane to foreboding. Aulaqi is only known to have replied twice, neither time urging violence.

FBI agents in the Washington field office (WFO) dismissed Hasan as a potential threat after a cursory investigation described as "slim" by San Diego investigators monitoring Aulaqi.

At one point in mid-2009, the Washington agent who conducted the investigation reportedly told an impatient San Diego colleague that the Washington office "doesn't go out and interview every Muslim guy who visits extremist websites," adding the subject is "politically sensitive for WFO."

The Washington agent does not recall that conversation, according to the Webster report.

There were ample warnings that Hasan was growing more radicalized and posed a danger, said Rep. Frank Wolf, R-Va., chairman of the appropriations subcommittee on commerce, justice and science, which held the hearing on the Webster report.

"I am concerned that there were warning signs, and that with more aggressive investigation, there is a chance that this incident could have been prevented," Wolf said.

"I am further concerned that the reason for less aggressive investigation may have been political sensitivities in the Washington Field Office, and maybe even the FBI's own investigating guidelines," Wolf said.

Wolf added he has been contacted by several FBI agents who fear their careers may be harmed if they are too aggressive in pursuing potential Muslim extremists because of political correctness at the bureau.

Mark Giuliano, executive assistant director of the FBI's national security branch, acknowledged the investigation of Hasan was not aggressive enough.

The most notable flaw was that Washington agents did not interview Hasan because they did not believe he posed a terrorist risk after reviewing his personnel files and other records.

"I personally do not believe that political correctness had anything to do with this determination," Giuliano said.

Giuliano repeatedly said the Webster report concluded that political correctness was not a factor in the skimpy investigation of Hasan by the Washington field office.

The report does not say that or address the issue. Eventually, Wolf pointed that out, forcing Giuliano to correct himself.

The Webster report says the Washington agent's decision not to interview Hasan was based on factors such as his positive Army fitness reports, recent promotion to major and the fact he was not trying to hide his identity.

Also, at the time of the Fort Hood shooting, Aulaqi was known as a radical Muslim leader but had not openly advocated violence.

Mark Flatten is a member of The Washington Examiner special reporting team.