FORT WORTH, Texas — The pictures of 7-week-old baby Jax, with wires and tubes all over his little body, tell part of the tragic story. But a newly-released probable cause affidavit tells even more.

20-year-old Kaleb Eisenmann sits in the Parker County Jail in a single cell, arrested for a first-degree felony in baby Jax's injury. The Parker County sheriff said Eisenmann is on suicide watch.

"Angry, hurt, confused," the baby's maternal grandmother Michelle Aaron told WFAA Sunday. "I don’t understand why."

The baby's family says Eisenmann was dating Jax's mother and was watching Jax on Valentine's Day.

"He was babysitting," Aaron said. "My daughter was working, she’d just gotten a job at Dickey's Barbecue."

But according to the affidavit, Eisenmann became "frustrated with the baby" and that he had "jerked the baby up out of an infant swing too hard." That caused "the infant's head to jerk back."

Eisenmann then sat the baby down "really kind of hard" in the baby's bed, according to the affidavit.

The document says the baby had a brain injury, a neck injury "consistent with the infant's head being jerked back and forth in a forceful manner" and bruising along his waist line.

The sheriff's office says the baby had a seizure on his way to the hospital.

"If he was so angry, why didn’t he just set him down and let him cry?" Aaron said Sunday. "He didn’t have to hurt him."

Tuesday, the baby's great-aunt said Jax is still fighting, and the baby's mother and grandmother remain by his side. They ask for continued prayers.

"We’re praying God can perform miracles," Aaron said.