New York (CNN) -- A decorated U.S. Army soldier allegedly admitted he killed a 4-month-old girl he and his wife were trying to adopt, police said Friday.

Pfc. Jeffrey Sliker was charged in the death of Laurne Clark, also known as Mollie Sliker, after police responded to a call from the couple's house on Wednesday, according to Julie Call, a court spokeswoman in Watertown, New York.

Police say they found the infant with no obvious external injuries, but an autopsy later revealed blunt force trauma to the skull as the cause of death, according to Watertown Police spokesman Frank Derrigo.

Upon questioning, Sliker allegedly admitted causing the injury, Derrigo said.

Sliker's brother, James, says he can't believe his brother was responsible for the infant's death.

"I don't see him ever trying to hurt someone, especially his own daughter." he told CNN affiliate WWNY. "I just don't understand what happened. He's not the brother that I know."

The 23-year-old suspect earned recognition for meritorious service while in Afghanistan.

He was arraigned Friday morning in Watertown City Court and is being held without bail.

Sliker's attorney could not immediately be reached for comment.

Sliker is expected to face a preliminary hearing in Jefferson County Court early next week.