FORT WORTH -- The man arrested and charged with murdering a Fort Worth teenager says he is innocent.

"I know nothing about it," said James Murphy, 37.

Murphy spoke to News 8 from inside the Mansfield Jail, where he's being held on a capital murder charge and a second charge of aggravated robbery.

Police arrested him yesterday, a relief to the family of the victim, Chaz Gilley.

<p>Chaz Gilley</p>

"He's off the streets where he cannot do this to another child," said Chesala Markham, Gilley's mother. "At the same time, it's extremely painful, because now I know the monster that did this to us."

Markham says her son was a goofy and fun-loving young man who had recently started a job at Goodwill in Fort Worth. She says on Oct. 7 just before 5 p.m., Gilley rode his bike to a nearby Walmart to cash his first paycheck.

"He was excited," she recalled. "He was going to buy a new cellphone, because he had dropped and cracked his screen."

But Gilley never made it home. On the bike ride back from Walmart, she says, he was run over by a car and then shot twice.

Doctors tried to save him, but he died the next day.

"I'm never going to get to kiss my son's face again," Markham said through tears.

She says police detectives contacted her to let her know of Murphy's arrest, and told her that her son was targeted in Walmart for the money he was carrying.

James Murph

"Probably about $400 in his pocket," Markham said. "It makes me sick."

Fort Worth police could not confirm those details and said that the investigation is ongoing.

Murphy does have a long criminal history, and court records show in 2007 he was charged with the murder of another Fort Worth teen, Kelvin Collier, who was 16 at the time.

But those charges were later dropped at the prosecutor's discretion. Wednesday, the Tarrant County District Attorney's Office said it was because the prosecutor did not feel there was sufficient evidence.

"It makes me angry, because had they worked harder, maybe if they dug deeper, maybe the could have found the evidence to put this man away," Markham said.

Now, the mother says she's fighting for two teenagers, and she's determined that James Murphy will see justice.

"No matter what I have to see, no matter what I have to hear, this man is going to see my face every single court date," she said.