Elizabeth Johnson, 23, is the key to finding out what happened the baby, but so far she has been no help.
Gabriel has been missing since December, when he was last seen with his mother.
With fewer leads coming in to police, Gabriel's father held a vigil in Scottsdale, Arizona on Sunday night to keep his son's face, and case, in the news.
"I want him back more than anything else," said Logan McQueary.
Gabriel was taken illegally on a cross-country bus trip by his mother, who lost legal custody of the child.
On the journey, Johnson took photos of Gabriel, who appeared groggy and holding a medicine dropper.
Then she sent a chilling text message to the father claiming to have killed the boy.
"She said, 'I stuffed him in a diaper bag, suffocated him, put him in a diaper bag, put him in a dumpster,'" said McQueary. "She said, 'You ruined my life and this is what you deserve.'"
When police tracked down and arrested Johnson in Florida, there was no sign of Gabriel. At that point she said the baby was alive, and that she gave the child to a random couple she met in a San Antonio, Texas park.
On Monday Johnson pleaded not guilty to kidnapping and abuse.
Investigators have been trying to walk a fine line between building a case against the mother, while also needing her cooperation.
So far, Johnson is telling detectives little.
For his part, Gabriel's father says he thinks his son is alive, and that Johnson is purposely trying to keep the baby from him by claiming she doesn't know where he is.
