BRUNSWICK, Ga. -

The mother of a baby gunned down in his stroller says she has no doubt a teenage suspect is the man who killed her 13-month-old son, but family members say he wasn't anywhere near the scene.

"That's definitely him," Sherry West said Saturday when she saw the jail mugshot of 17-year-old De'Marquise Elkins, who is charged as an adult with first-degree murder. Police also arrested a 14-year-old who has not been identified because he's a minor.

The Brunswick Police Department said Sunday that they got a tip that someone was crouched in the back seat of a vehicle as it drove away from the shooting Thursday. The Glynn County detective's division spent hours following up on the tip and eventually arrested the 14-year-old. The boy's statements led them to take Elkins into custody.

"We're trying to determine which one actually was the shooter," police spokesman Todd Rhodes said Saturday.

But West said she was certain the gunman was the older suspect. "He killed my baby, and he shot me, too," she said.

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On Thursday morning, West was pushing Antonio Santiago in his stroller after a trip to the post office. She said a teen, accompanied by a smaller boy, asked her for money.

"And he kept asking, and I just said, 'I don't have it.' And he said, 'Do you want me to kill your baby?' And I said, 'No, don't kill my baby!'" she said.

One of the teens fired four shots, then walked around to the stroller and shot the baby in the face.

De'Marquise Kareem Elkins Police announced the arrests of Elkins (pictured, right) and the 14-year-old Friday afternoon. But Elkins' older sister said her family knows he wasn't involved in the shooting.

"My brother wasn't anywhere near that area as far as we know — not the scene or the shooting," she said Saturday. She said she didn't know whether Elkins had a lawyer.

"He couldn't have done that to a little baby," she said. "My brother has a good heart."

She said her brother had been living in Atlanta and returned to Brunswick only a few months ago. Typically, he would come by her house in the morning and they'd go to breakfast. But Friday morning, police came to her door as her brother was approaching along the sidewalk.

"The police came pointing a Taser at him, telling him to get on the ground," she said. "He said, 'What are you getting me for? Can you tell me what I did?'"

Elkins' Facebook page give a different picture of the teen, seemingly portraying himself as a gang member and containing this recent post: "ME IN MY (expletive) A TURN UR BLO5K IN TO MURDER SCENE."

On Saturday, police released recordings of three 911 calls made by West's neighbors right after the shooting.

LISTEN: Brunswick 911 call

One caller, sobbing, tells the operator she heard three gunshots.

"Is the baby bleeding? How close are you to them? How old does the baby look?" asks the dispatcher.

"He's in a stroller, he's got to be a toddler," said the caller. "The baby is on the ground now. The woman is over the baby."