A Palmdale man pleaded not guilty this week to charges stemming from the beating death of his girlfriend’s 2-year-old daughter.

Matthew Albert Worthen, 23, is charged with one count each of murder and assault on a child causing death.

Worthen allegedly assaulted the toddler, who is identified in the criminal complaint as Zanai N., while the toddler was left in his care on Sept. 22.

The girl appeared to be having difficulty breathing when her mother returned home and was taken to a local hospital, where she died.