Major Nidal Malik Hasan, the US Army psychiatrist accused of killing 13 people in a shooting rampage at a military base in Texas, had been plotting the massacre for weeks, a British newspaper claimed on Sunday.

According to the 'Daily Star', Maj Malik Hasan bought a Belgian-made FN 5.7 mm semi-automatic pistol at a gun shop less than 15 miles from Fort Hood military base in September, indicating he was hatching a plan since then.

Moreover, the US Army officer also gave notice to the owner of his apartment block two weeks ago that he would be moving out by November 7 and gave away all his belongings, the report said.

Major Malik Hasan was on Sunday taken off the ventilator even as investigators have been looking for clues to ascertain the motive for the horrific killings.

According to doctors, the 39-year-old who went into coma after being shot several times in exchange of fire, is now in a stable condition at the Brooke Army Medical Center, where he has been taken off ventilator.

Federal and military officials, probing the motive behind Hasan's killing spree, have interviewed almost 170 witnesses as part of an intensive search for clues.

Computers, emails belonging to Maj Hasan have been seized to figure out if somebody may have been behind the Army psychiatrist's act.