SALT LAKE CITY — A 35-year-old Murray woman was charged Monday with first-degree murder in the September death of a 4-month-old baby.

According to documents filed in 3rd District Court, Jennifer Duran Martinez told police she was babysitting Kaysen Calhoun, as she had often done, for about two hours on Sept. 22, when she became "frustrated and stressed" that the boy would not stop crying. She then "picked him up and violently shook his head back and forth for an extended period of time," charges state. When the boy stopped breathing, Martinez called 911.

Calhoun was initially taken to Intermountain Medical Center and then to Primary Children's Medical Center, where he was taken off life support and died Sept. 24.

Doctors determined the boy had a fresh brain injury and several retinal hemorrhages in both of his eyes, which were later deemed by the medical examiner to be a common sign of a head injury. Calhoun was also found to have at least two rib fractures that likely occurred on different occasions, as one was in the process of healing, according to doctor's statements to police.

An autopsy to determine the ultimate cause of death is ongoing, but a medical examiner reported finding "nothing other than the apparently inflicted head injuries," as stated in court documents.

Martinez is charged with one count of murder, a first-degree felony. She was booked into the Salt Lake County Jail a couple days after the boy died and has been released on a $500,000 cash-only bail bond.

Wendy Leonard, Twitter: wendyleonards