MARIETTA, Ga. -

A teenager fatally shot a 13-month-old baby in a stroller in Brunswick when the child's mother did not immediately hand over her purse, a prosecutor said on the first day of the man's murder trial Tuesday, while a defense attorney suggested to a jury that the child's parents were somehow involved in the slaying.

De'Marquise Elkins is charged with murder and other offenses in the March 21 killing of the toddler, Antonio Santiago. Meanwhile, on Wednesday it was ruled that the second teen suspect will be allowed to testify against Elkins.

Jurors and spectators gasped and wiped tears from their eyes when Brunswick Judicial Circuit District Attorney Jackie Johnson began her arguments by showing photographs of the body of child lying on a blood-soaked blanket on an ambulance stretcher with a gunshot wound to his face.

"The young man took the gun and aimed it at Antonio's head and shot him right between the eyes," Johnson told jurors.

The child's mother, Sherry West, was shot in her leg while another bullet grazed her ear. Prosecutors have also accused Elkins of shooting Wilfredo Calix Flores outside a local church 10 days before the child was killed.

Antonio Santiago The broad-daylight killing of a toddler this spring on a downtown Brunswick sidewalk drew national attention, and the trial was moved to the Atlanta suburbs because of the extensive publicity the case received locally. In opening statements, Johnson told jurors that both shootings started off as robberies.

"When it didn't happen immediately, as Mr. Elkins thought it should, his reaction was to shoot," Johnson alleged.

The prosecutor said Elkins and an accomplice, 15-year-old Dominique Lang, stopped the mother and child as they returned home from the post office. Johnson said that Elkins pointed a small .22-caliber revolver at West and demanded her money. West did not immediately hand over her purse and the child was shot.

Bystanders and rescue workers were unable to revive the child, who was pronounced dead at the scene.

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Lang is also charged as an adult with murder but will be tried separately. Authorities said Lang identified Elkins as the shooter and is expected to testify at the ongoing trial.

Defense attorney Jonathan Lockwood suggested that Antonio's parents were somehow involved in his death, though he did not provide a precise motive or further explain that theory. He said that no one in the neighborhood saw or heard anyone fleeing the scene of the shooting.

He also questioned whether police focused their investigation too soon on the wrong suspects. He said that West tried to collect on a life insurance policy shortly after her son's death.

"The police were under a great deal of pressure to see that the matter was resolved as vacation season was not far away," Lockwood said.

Lockwood said the child's parents both had gunshot residue on their hands. A report filed earlier by the Georgia Bureau of Investigation said that gunshot residue can wind up on shooting victims. The child's father, Louis Santiago, said during an initial court hearing that he touched the bullet wound on West's leg before his hands were swabbed.

Prosecutors said information from Elkins' mother and sister led investigators to a pond where they found a .22-caliber revolver. Elkins' mother, Karimah Elkins, is standing trial alongside her son on charges of evidence tampering and lying to police. Elkins' sister was also charged with evidence tampering.

Elkins on trial An attorney for Karimah Elkins, J. Wrix McIlvaine, said police had violated her rights and that she was not involved in the killing.

McIlvaine said, "None of these people had anything to do with the shooting of a child."

Cross-examination continued Wednesday as of one of the officers who responded to the shooting took the stand. The defense spent most of the morning questioning Brunswick police detective Angela Smith, who was one of the first to interview the child's mother.

Smith testified that West had trouble identifying Lang. Smith also admitted that West told her she suffered from mental illness.

The defense attempted to use those claims to discredit West's ability to identify Elkins as the shooter.

Defense attorneys tried to show with their questioning that police rushed to make an arrest without exploring other possible motives.

Smith testified that West was considered somewhat of a suspect at the time of the shooting.

"What part of your standard operating procedure does it say you consider someone a suspect?" attorney Kevin Gough asked Smith.

"There isn't, Mr. Gough, but one would have to assume while you're working the case to start with who you have in front of you," Smith said.

"What steps did you take to to ensure that she's not responsible for the killing of her child?" Gough said.

"Just the interview with Ms. West," Smith said.

"And what steps did you take to ensure Louis Santiago didn't have anything to do with it?" Gough said.

"I spoke with Mr. Santiago very briefly and that was it," Smith said.

Gough said police rushed to make an arrest because of the public outcry, when there where no witnesses of the shooting except West.

The defense also tried to discredit West's ability to identify the suspects because she suffers from post-traumatic stress disorder, paranoia and bipolar disorder.

The detective testified that she was aware that West has a mental disorder, but it didn't raise any red flags.

Lang took the stand while jurors were at lunch.

His interrogation video was played in court without the jury present, and in the video he was looking at photos. Police asked him to point out the shooter, but he did not seem 100 percent sure which photo was of De'Marquise Elkins. To that point, the defense wanted Lang's testimony to not be admitted in front of the jury, but the judge denied that motion.

"You got to let my auntie come down here because she seen him more," Lang said in the interrogation video. "I was just thinking about that baby. That's all I was thinking about. I swear that kind of looks like him, sir."

When questioned by prosecutors, Lang described the red shirt and dark that Elkins had on that day. Lang testified that he and Elkins were walking together the before the shooting. He described the robbery attempt between Elkins and West.

"He kept asking for her purse and she kept refusing," Lang said.

After West refused, "he reached in his pocket for his gun," Lang said. "He slapped her with the gun. He threatened the baby. He went around the stroller. She came around the other side and he shot."

Lang is expected to testify in front of the jury before the end of the week.

If convicted, Elkins will not face the death penalty because he was 17 at the time of the killing -- too young under Georgia law to be executed.