Breaking news update: Officer Johannes Mehserle has resigned.

Although BART police officer Johannes Mehserle has yet to give an official statement to his superiors, BART investigators are speculating whether he meant to pull out his Taser instead of his firearm when he shot and killed an unarmed man in the back on New Year’s Day.

However, BART police officials are unable to confirm whether he was even carrying a Taser when he killed Oscar Grant in an incident caught on citizen video, according to the Oakland Tribune.

In fact, they’ve only started to train their officers to use Taser guns within the last three months and don’t even have enough to supply every officer. Also, they are required to carry the Tasers on their belt on the opposite side of their firearms.

Furthermore, the department-issued firearm is a Sig-Sauer 40-caliber, which according to the Tribune, weighs nearly three times as much as the department-issued Taser X26. It is also two inches taller.

Although the Tribune doesn’t specify exactly which Sig Sauer model the officer was using that night, the most common police-issued firearm is the P226, according to the company’s website.

Regardless if he thought he was reaching for his taser, Mehserle is still guilty of homicide, according to John Burris, the attorney representing Grant’s family who filed a $25 million claim against BART on Tuesday.

“If he thought he was reaching for a Taser and pulled a gun, that’s negligent. That would be involuntary manslaughter, a negligent homicide,” Burris said. “If he didn’t have any Taser on him … that’s an intentional killing: second-degree murder.”

If it turns out that Mehserle claims he meant to use his Taser instead of his firearm, it wouldn’t be the first time a California police officer shot and killed an unarmed suspect with a firearm, then claimed to have meant to use the Taser.

In 2002, Madera Police officer Marcy Noriega shot and killed a 24-year-old man as he sat handuffced in the backseat of her car. Noriega claimed she meant to subdue Everardo Torres with her Taser as he allegedly kicked at the vehicle’s windows.

The officer was not criminally charged but a civil case is pending, according to the San Francisco Chronicle.

In the latest case, Mehserle, 27, a two-year officer of the Bay Area Rapid Transit Police Department, is not legally required to give a statement about the New Year’s Day incident because he is protected by the Fifth Amendment.

However, by not giving a statement, he could be terminated from the police department for failure to follow departmental procedure.