Although Gabriel looks healthy and active in the pictures, lying on a bed with toys and a pacifier, investigators say they worry that Gabriel appears to be holding a medicine dropper in two of the photos.
"Elizabeth told me to give him a bottle in about an hour, and then her exact words were to 'give him more medicine if he started crying to shut him up,'" Urias said.
"Gabriel wasn't acting like a normal baby," she said. "He was acting scared, he didn't want to play. He acted like he was sad."
The photographs were found in Johnson's camera following her arrest Dec. 29 in Miami.
Urias also said she found a large knife next to the bed in the motel room.
"It looked like a butcher type of knife and, you know, I thought that was weird because why would she have it next to her bed? It's something that would belong in the kitchen," Urias said.
The photographs were date-stamped Dec. 26, the last day anyone saw Gabriel.
Johnson described the couple as white and in their 30s. The man was tall with short black hair, and the woman was 5 feet 3 inches tall, with long blond hair.
Johnson said the two looked trustworthy and brought their own car seat ,and that they said they could keep baby Gabriel without anyone noticing.
"Yes, I'm sure he's alive," Johnson said in a jailhouse interview.
Gabriel's grandfather, Frank McQueary, said that is all the more reason to be vigilant.
"That next door neighbor may be buying stuff for a baby, and they didn't have a baby before," he said. "Let somebody know."
Anyone with information about Gabriel Johnson is asked to call the Tempe Police Department at (480) 350-8311.
ABC News' Deborah Johnson and Lee Ferran contributed to this report.