Trayvon Martin's parents Sybrina Fulton, Tracy Martin "at ease" after George Zimmerman's arrest

(CBS News) The parents of an unarmed Florida teenager fatally shot by a neighborhood watch volunteer in February said on "CBS This Morning" Thursday that they were "at ease," "excited" and "overwhelmed" by the gunman's arrest Wednesday on a murder charge.

Sybrina Fulton and Tracy Martin, the mother and father of teenager Trayvon Martin, told Erica Hill, Gayle King and Charlie Rose how they felt knowing that George Zimmerman spent the night in a Florida jail after a special prosecutor charged him with second-degree murder in Martin's death.

"I felt a little bit at ease knowing that he had been apprehended, that he had turned himself in," said Tracy Martin, "and knowing that he wouldn't be able to possess a firearm after being arrested any more, knowing that he wouldn't be able to take another 17-year-old's life."

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Zimmerman is expected to plead not guilty citing Florida's so-called "stand your ground" law in court later Thursday. Zimmerman's brother and father have been outspoken in defending him, going on television and saying Martin attacked Zimmerman, who used his weapon in self-defense. Hours after the February shooting, Zimmerman was released, which Fulton strongly opposed.

"We just want people to know that if you shoot someone that is unarmed that you should be arrested," said Fulton. "The evidence can play out once you get to court, but you should be arrested. This was a minor. This was not another adult, and my son was unarmed."

The arrest comes after the shooting attracted national attention with marches and protests calling for Zimmerman's arrest.

"We are, you know, overwhelmed that he was arrested because this is what we've been fighting for for 44 days," said Fulton, "and we were just excited to hear that he was arrested."

Above, watch Trayvon Martin's parents explain what George Zimmerman's arrest means to them