The family of Trayvon Martin is renewing its call for the arrest of George Zimmerman, the man who killed the teen in what he called an act of self-defense, after listening to 911 calls related to the teen's death last month.

A prayer vigil and walk to the steps of the Titusville Courthouse from St. James AME Church is planned Sunday afternoon at 3 p.m.

Meanwhile, a memorial outside of the gated community where Martin was killed continues to grow.

Bryce Roberts, 15, lives within walking distance in Sanford. He never knew Trayvon, but felt it was important to recognize him with a silent, but powerful message on a homemade sign that read “I could've have been Trayvon.”

“I just thought it was really sad that this kid had to leave earth for really no apparent reason,” Bryce Roberts explained.

Bryce's mother, Jennifer Roberts, believes the message on the sign is true.

“That my son could have been Trayvon, absolutely. He is two years younger than Trayvon. It could have happened to him. There is no telling of what could have happened to him,” said Jennifer Roberts.

“People at school talk about it a lot. Teachers, friends, people have stuff to say about it, (they) think it's really sad and not right what happened,” the 15-year-old Roberts continued.

Just a day earlier, the family arrived at Sanford City Hall Friday evening to hear the 911 tapes. They were expected to speak afterward, but the family's attorneys said the parents were so overcome with grief after what they heard on the tapes, they could not speak.

"It is shocking when you hear these 911 tapes," said attorney Ben Crump. "It was far worse than they thought it was going to be."

Zimmerman is a neighborhood watch volunteer who was on patrol when he encountered Trayvon. Zimmerman admitted to the shooting.

The attorney says in at least one 911 call two shots are heard -- one distant shot is heard, then a second, louder shot is heard. Throughout the call you can hear someone screaming for help until the second shot, then the screaming stops.

Attorney Natalie Jackson says it is clear that Zimmerman fired a warning shot, then a kill shot.

"This is an insult to this family," Jackson said. "This was not self-defense, this was not manslaughter, this was murder."

Crump also accused the Sanford Police Department of lying regarding Trayvon's cell phone. Police said they had to get a subpeona to get the phone, but

Crump said police have had the cell phone the entire time, and the family never had the phone.

Zimmerman's 911 call

Among the calls released Friday is the call George Zimmerman made to police when he spotted Trayvon Martin. He starts off by saying that there have been some break-ins in the neighborhood, and that he spotted a "real suspicious guy" in the area. He said the guy looks like he's up to no good, and may even be on drugs. He also makes note that he has his hand in his waistband.

When the dispatcher says that he is sending an officer over, Zimmerman says "these [expletive] always get away."

At one point the dispatcher also asks if Zimmerman is following the suspect. Zimmerman says yes. The dispatcher asks him not to do that.

Witnesses coming forward

Three witnesses, including two women, have come forward, claiming they witnessed the deadly shooting.

Mary Cutcher and her roommate said they heard the 17-year-old crying and pleading for his life.

Then, they said they heard the gunshot that killed him. Cutcher and her roommate said they rushed outside to see Zimmerman standing over Trayvon's body.

Standing with the teen's family and their attorneys Friday morning, the two witnesses said they believe Zimmerman murdered the boy, and believe police have not done enough in their investigation.

Sanford police, however, said Cutcher told a different story to the media than what she told them.

In a statement released Thursday, Sanford police public information officer Sgt. David Morgenstern said:

"According to investigators notes she was called on February 29th, March 1st, and on March 2nd when she and her roommate finally came in to be interviewed. The information she provided in her sworn statements regarding the actions of Zimmerman were consistent with the information Zimmerman provided."

"I have no reason to lie," said Cutcher. "I don't know this family. I'm only trying to help, and I think that they are trying to cover up something -- that they made a mistake -- and honestly, I feel like they're taking the light off of them and trying to discredit my statements."

"Just to know that regardless of what happens, there's still good people in this world," said Trayvon's mother, Sybria Fulton, regarding Cutcher. "I'm so very hurt by this whole situation. It's a nightmare, and I don't understand why this man has not been arrested, at least charged, and let a judge and a jury decide if he's guilty."

Trayvon's parents said their son was unarmed when Zimmerman confronted him, because he thought the teen was suspicious. They said Trayvon was returning to a relative's home from the store with a bag of Skittles.

As of noon Friday, more than 240,000 people have signed a petition calling for Zimmerman's arrest.

The State Attorney's Office is reviewing the case.

Bringing in the Justice Dept.

The family's attorneys say the family no longer trusts the Sanford Police Dept., and want the US Justice Department to take over the case.

The tapes were released on the same day Sanford Police Chief Bill Lee met with Congresswoman Corrine Brown, D-Jacksonville, and Sanford Mayor Jeff Triplett Friday. They said Lee told them he welcomed a federal investigation by the U.S. attorney general and US Dept. of Justice.

"I at this point don't trust and I need an independent," Brown said. "I feel that the United States Justice Department is independent because I think some things should have been done, didn't happen. So we need to make sure it happens.”

Rev. Al Sharpton to voice support for justice

The Reverend Al Sharpton announced Saturday morning he will come to Sanford Thursday evening to hold a support rally to justice at the First Shiloh Baptist Church.

The church is located at 700 South Elm Avenue. The event will begin at 7 p.m.

During the last week, Sharpton spoke out in support of the Martin family.

Meanwhile, Dr. L Ronald Durham, who is a pastor at Greater Friendship Baptish Church in Daytona Beach is organizing the rally. Durham told News 13 that Sharpton did not decide to come on his own. He said Sharpton was asked to come by Martin's family and attorneys.

Pastor Durham said the rally has only been in the works for a few days, but they are expecting several hundred people to attend the event.