The transit officer who shot and killed an unarmed man may have mistakenly pulled his service pistol instead of a stun gun, according to documents filed by his lawyer Friday.

Attorney Michael Rains made the argument in urging a judge to grant bail for 27-year-old Johannes Mehserle. Alameda County Superior Court Judge Morris Jacobson later set bail at $3 million.

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Mehserle has pleaded not guilty to one count of murder in the death of 22-year-old Oscar Grant, who was killed early New Year's Day. Cell phone videos of the incident, widely viewed on the Internet, showed the officer standing over Grant as he was lying facedown on a train platform and firing one shot into the man's back.

Grant died of the gunshot wound to his torso.

In a court filing Friday, Rains said witness accounts indicate that Mehserle meant to draw his Taser, but instead pulled his pistol. The lawyer blamed inexperience by the young officer, who passed his Taser user certification test on Dec. 3.

"The bulk of the discovery, including witness and officer statements, seem to indicate that this young officer, who carried a taser for only a few shifts prior to this event, may have mistakenly deployed his service pistol rather than his taser, thus negating any criminal intent," Rains wrote.

The court documents contain statements and reports from several officers who were on the platform with Mehserle at the time of the shooting.

The officers — who had just pulled several men, including Grant, from a Bay Area Rapid Transit train after reports of fighting — described the scene as chaotic and confusing.

According to a statement from Officer Tony Pirone, Mehserle told Grant to stop resisting and put his hands behind his back. Then, according to Pirone's statement, Mehserle said: "I'm going to taze him, I'm going to taze him. I can't get his arms. He won't give me his arms. His hands are going for his waistband."

Pirone said he didn't know if Grant was armed, but said Mehserle told him he had believed Grant may have had a weapon.