WEST VALLEY CITY — A teenager is in juvenile detention after allegedly shaking and critically injuring a baby Tuesday, police said.

About 8:30 p.m., police were called to a home at Shadowbrook Apartments in the area of 3840 S. Redwood Road on the report of an unresponsive baby, said West Valley Police Lt. Kent Stokes.

When officers arrived they performed CPR on the 4-month-old until medical crews arrived and took her to Primary Children's Hospital, Stokes said. The baby remained there in critical condition as of Thursday evening.

At the hospital, a doctor noticed signs of shaken baby syndrome. Detectives learned the infant was being baby-sat by a 16-year-old boy at the time of the incident, according to Stokes.

The boy had been there when police arrived Tuesday evening, Stokes said. The infant's parents weren't there at the time the baby was injured, according to the lieutenant.

Police interviewed the teen and he was booked into juvenile detention Wednesday night, Stokes said. He declined to discuss what officers learned in that interview in further detail. However, he said "there was enough information obtained at the time for probable cause to book him on child abuse charges."

"It’s a very sensitive and tragic event for the parents and the officers as well," Stokes said.

As the family waited in the hospital Thursday, they said the baby, named Adalyn, might not survive.

"None of us can wrap our heads around any of this," said Adalyn's great aunt, Elena Ratcliffe. She spoke on behalf of the family, who asked that the baby's full name not be released.

In an earlier email to the Deseret News, Ratcliffe said Adalyn's parents were picking her up from the babysitter's house when they noticed she wasn't breathing. The father started performing CPR while the mother called 911, according to Ratcliffe.

"They've tried to see if there has been any brain wave activity, which there is none," she said.

The alleged abuse by the babysitter has left the family in shock.

"You'd never think that something so small, somebody could do something so horrible," Ratcliffe said.

According to the great aunt, if Adalyn doesn't live, her organs will be donated.