Rather, they have come to believe that Maj. Nidal Malik Hasan, the Army psychiatrist accused in the shootings, acted out under a welter of emotional, ideological and religious pressures, according to interviews with federal officials who have been briefed on the inquiry.

Investigators have not ruled out the possibility that Major Hasan believed he was carrying out an extremist’s suicide mission.

The investigators, working with behavioral experts, suggested that he may have long suffered from emotional problems that were exacerbated by the tensions of his work with veterans of the wars in Iraq and Afghanistan who returned home with serious psychiatric problems.

They said his counseling activities with the veterans appear to have further fueled his anger and hardened his increasingly militant views at the same time that he seemed to move toward more extreme religious beliefs - all of which boiled over as he faced being shipped overseas, an assignment he bitterly opposed.