Reynaldo Sanchez will find out in April how long he will have to go to prison for killing his 3-month-old son Adrien in December 2011.

The 20-year-old Sanchez pleaded guilty Wednesday to a first degree murder charge as part of a plea agreement with Ada County prosecutors, who will ask for a life sentence for Sanchez, which would allow him to ask for parole after serving 20 years.

Sanchez can ask for a lesser sentence. Anyone convicted of first degree murder has to serve at least 10 years in prison.

Fourth District Judge Timothy Hansen will sentence Sanchez on April 9. Hansen does not have to follow the plea agreement. First degree murder is punishable by up to life in prison without parole.

Sanchez was supposed to start a jury trial on Feb. 4. It looked like the case was about to go to trial and lawyers were working a jury questionnaire when Sanchez asked for a new hearing earlier this month and changed his plea Wednesday.

Ada County Coroner’s reports show that three-month-old Adrien Sanchez died from blunt force trauma injuries to the head and the manner of the infant’s death was a homicide — and Ada County Sheriff’s deputies say Sanchez is responsible.

Reynaldo "Lucas" Sanchez has been in the Ada County Jail shortly after paramedics found the boy critically injured at a southeast Boise home the morning of Dec. 16, 2011.

Paramedics were sent to the home after a caller said a baby had fallen out of an infant bouncy seat and was hurt.

Paramedics first took the baby to St. Luke’s Hospital in Meridian for treatment of significant injuries to his head and body, before he was moved to St. Luke’s in Boise. The child died several hours later, according to reports.

Detectives determined the injuries were not consistent with a fall from a bouncy seat, but had, in fact, been caused by the child’s father, according to sheriff’s reports.

Sheriff’s officials say the infant was in Sanchez’s care at the time of the 911 call. Detectives say Sanchez called two other people who live at the home and told them the baby was hurt after falling out of the baby seat.

Those people came back to the house, saw the baby’s injuries, and immediately called 911, according to reports.

Prosecutors do not need to prove premeditation to charge first degree murder when the victim is under the age of 12. In the case of Sanchez, prosecutors had to prove that he committed an aggravated battery that led to the death of Adrien.