Dad admits to shaking premature infant son, now in critical condition; baby in dad's "custody" when abuse happened (Spartansburg County, South Carolina)

What was going on here? What does it mean to say that the baby was in dad's "custody" when the abuse happened? Was he babysitting while Mom stepped out for a gallon of milk? Was he one of those deadbeat "stay-at-home" dads, the kind who can't or won't get a job and can't deal with infant care either? Or was this premature infant actually being subjected to a custody/visitation agreement?

Notice that this baby had only been home from the hospital for FOUR FREAKING DAYS before Daddy "allegedly" went off on him.

Dad is identified as JACOB SHATTUCK.

http://www.wyff4.com/news/local-news/spartanburg-cherokee-news/Deputies-Father-accused-of-abusing-premature-child/-/9324158/15461744/-/o639gh/-/index.html

Deputies: Father admitted to shaking premature infant

UPDATED 8:02 PM EDT Jul 10, 2012

SPARTANBURG COUNTY, S.C. - An Upstate father is accused of critically injuring his infant son, according to an arrest warrant.

Jacob Shattuck is charged with felony child abuse.

Spartanburg County deputies were called to Greenville Memorial Hospital on July 9 about a baby that was admitted to pediatric intensive care with a non-accidental head trauma, according to an incident report.

The report said the infant had been in the ICU from April 6 to July 5 because the child was born 10 weeks premature.

The warrants said the baby was in Shattuck’s custody when the abuse happened.

Deputies said when they interviewed Shattuck he admitted to shaking the infant and said he knew what he had done was wrong.

According to deputies, the baby is in critical condition. Shattuck is being held with bond set at $100,000.