MIAMI (CBS4) – The family of a Miami teen killed in Central Florida is now calling for the FBI to take over the investigation into their son’s death. They, along with their attorneys say Sanford police are trying to discredit two witnesses who assert that Trayvon Martin’s death was murder, not self-defense. Now, thousands of people across the country are demanding an arrest.

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Mary Cutcher and Selma Mora Lamilla have been thrust into the media spotlight because of what they heard and saw the night of February 26th in their Sanford gated community. They spoke out in a news conference Friday morning.

“I heard the crying, it was a little boy. As soon as the gun went off, the crying stopped,” said Cutcher.

They believe the cries came from Martin, 17, before their neighborhood watch captain, 28-year-old George Zimmerman.

“I look at this guy on top of the body, and I ask him what’s going on?” recalled Mora Lamilla.

“The boy was face down, his face was in the grass.” added Cutcher.

Zimmerman says Martin attacked him and he shot in self defense. Martin was not armed. Police handed the case over to the Brevard Seminole State Attorney’s office to investigate without making an arrest.

“We believe in our hearts 100% that it was not self defense,” countered Cutcher.

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Both women accuse the Sanford police detectives of failing to contact them for several days, after they reached out repeatedly and said they were witnesses.

Also, Cutcher bristles at the Sanford police chief’s recent statement to the press that her story was inconsistent.

“I have no reason to lie. I don’t know this family, I’m only trying to help. I think (police) are trying to cover up something that they made a mistake.”

After international attention on the case, more than 240-thousand people have signed an online petition at social networking site demanding an arrest.

“People have signed from every state in the country and internationally as well…In just a few days it’s become one of the largest and fastest growing campaigns in history,” site manager Jon Perri told CBS4’s Natalia Zea.

Martin’s parents hope the pressure works. And after hearing from the witnesses they now want the feds to take over the investigation.

“I feel betrayed by the Sanford Police Department and there’s no way I can still trust them in investigating this crime,” said Martin’s father Tracy.

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At this point Sanford police are not commenting on the allegations made by those witnesses. George Zimmerman’s father gave an Orlando newspaper a letter that said his son acted in self-defense and that he is not a racist. The letter also said his son has been receiving death threats and moved out of his home.