(CBS News) The neighborhood watch volunteer who shot 17-year-old Trayvon Martin was arrested and charged with second-degree murder Wednesday after months of mounting tensions and protests across the country. CBS News anchor Scott Pelley spoke with senior correspondent John Miller and former assistant FBI director Jack Ford about the charges. Trayvon Martin's mom: "We simply wanted an arrest" Zimmerman charged with 2nd-degree murder PELLEY: Jack, why second-degree murder? FORD: Here's the thing: first-degree murder is all about premeditation. That means you intend to kill somebody. Even if you develop that intention just a split second before you did it and you follow through it. Second-degree murder doesn't have the premeditation. So you're not intending to kill someone, you may have intended to hurt them badly and they die as a result, but it's the absence of that premeditation that drops it down a notch. PELLEY: This case has been under review for weeks but there seemed to be a rush to get to this news conference today. MILLER: Well, two things play into that. One is - and, as Jack points out - they clearly had to have developed some new evidence in their reinvestigation of this that brought them to the level that they could bring a murder-two charge where that was not at all clear to police on the first night. But the second thing is once (Zimmerman's) lawyers went out yesterday and said, "We've lost touch with our client," if you're the prosecutors or the investigators you're going to say, "I want to know where this guy is. I want to put eyes on that place. I want to be able to have him in my hands because we can't have this turn into a fugitive case at this stage.' PELLEY: Now was the time to move from their perspective. Jack, how high is the mountain that the prosecutor has set for herself. FORD: Higher than usual. Usually prosecution has the burden of proof. Here they have to prove the elements of second-degree murder, but then they have to deal with the self-defense, the Florida self-defense, the stand your ground self-defense, which means you don't have to run if you're in the midst of a conflict before using deadly force. So the defense is going to say that George Zimmerman felt he was in fear for his life and that's why he resorted to deadly force and essentially the prosecution is going to have to disprove that inside the courtroom.