FORT WORTH, Texas -- Police have a arrested a second suspect in connection with the murder of a Fort Worth teen last month, and according to an arrest affidavit they were "laughing and bragging" about their crime.

Lajerrian Morgan, 24, was arrested Wednesday and charged with capital murder. A few weeks ago, James Murphy, 37, was arrested and also charged with capital murder.

"It's senseless; they did it for nothing," said Chesala Markham, mother of victim Chaz Gilley.

Gilley, 18, was gunned down in broad daylight on East Berry Street in Fort Worth. He was riding his bike home from Wal-Mart, where his mother said he had gone to cash a $400 paycheck.

"They killed my boy because they wanted what he had, and they didn't want to earn it themselves," Markham said.

In a jailhouse interview three weeks ago, Murphy denied any knowledge about the crime.

"I can't tell you something I know nothing about," he said.

But an arrest warrant affidavit says otherwise. An informant told police that Murphy and another Blood gang member were selling drugs at the apartment complex where Chaz Gilley lived with his family.

"They saw a 'white boy' looking at his check," the informant told police, and followed him to Wal-Mart "and waiting for him to cash his check."

Police say security video from inside Wal-Mart shows two men shadowing Gilley and watching him count money. The video then shows Gilley departing the store on bicycle with the men following in a black car.

According to the affidavit, the men used the car to knock him off his bike, and then they chased him and shot in multiple times as he tried to run away.

The informant said that a few days later, they were "laughing and bragging" about the crime.

"To go around bragging about it to other people," Markham said with tears in her eyes.

Gilley flagged down help and was taken to the hospital, but doctors were not able to save him.

"You took somebody's life. It's not a joke, it's not a game," Markham said. "My son will never grow up. He'll never have a family."

Now, Markham is determined that Murphy and Morgan pay. She vows that she'll be in the courtroom during any trial to come, and she wants them to face the death penalty for taking her son's life and then laughing about it.

"To me, they're going to get it easy compared to what my son had," she said. "My son lived the last minutes of his life in fear and in pain."