Now to Charleston, south Carolina, where police officer Michael Slager is on trial for a fatal shooting. He took the stand on Tuesday breaking down during his testimony. ABC's Steve osunsami is there in Charleston with the details and reaction. Good morning, Steve. Reporter: Good morning to you, robin. This case could go to the jury today. We could hear closing arguments this afternoon. Michael Slager didn't have to testify. But he clearly wanted to tell his own story in his own words. At times he was tearful. My family has been destroyed by this. The Scott's family has been destroyed by this. It's horrible. Reporter: Former north Charleston police officer Michael Slager was here on the witness stand trying to convince jurors he's not a murderer saying that he killed Walter Scott in 2015 because at the time he says he felt threatened. And at that point I made the decision to use lethal force because Mr. Scott never stopped, he's always dangerous. Reporter: But prosecuted asked how dangerous could Scott have been as he was running away from the officer unarmed. They even made Slager stand up and hold a tape ruler to show how far Scott ran before Slager started firing. It was 18 feet. I didn't know what was going on with all that so I fired my firearm until the threat was stopped. Reporter: Shortly after the shooting Slager told investigators he thought Scott was running away with his taser. On the witness stand he said he now knows that's not true. That it fell to the ground. Slager says the two fought over the taser in a struggle that happened before the cell phone recording. But he had trouble explaining what he's seen doing here. Picking up the taser from one location and moving it closer to Scott's body. I don't know why I dropped it on the ground but I did pick it up seconds later. Was it because I was policing my gear? I can't even answer to that. Reporter: Lawyers for Scott's family says it looks to them like Slager was planting evidence. You always wonder why exactly did he run back and pick it up? And then actually drop it by Mr. Scott's dead body. Reporter: It is possible the court could take a field trip to the crime scene today. Slager is pleading not guilty. If he is convicted he could get up to life in prison. Robin. Keeping a close eye on this. Michael.