taser, his muscle memory made him fire. that's the theory and as you'll see shortly, not everyone buys it. whether you buy it or not, though this is not the first such incident as our randi kaye explains. >> reporter: 2009 on a train station platform in oakland, california. 22-year-old oscar grant gets into a scuffle with b.a.r.t. transit police. officer johannes mehserle and another officer try to subdue grant. at some point, officer mehserle announces, i'm going to taze him, and then fires. trouble is he didn't use his trarz. he'd mistakenly grabbed his semi-automatic handgun, firing one shot into oscar grant's back killing him. protests erupted. how could a police officer have made such a fatal error? perhaps because of something called slips and capture, a psychological stress phenomenon experts say causes a person to slip from their intended path only to be captured by a