RELATED: Walnut Creek homicide victim identified
Gregory Prokopowicz, 38, entered the plea against the advice of his public defender who wanted to delay the arraignment until Thursday.
Prokopowicz is accused of shooting 47-year-old Roselyn Policarpio near Larkey Park last Thursday afternoon.
RELATED: Martinez standoff ends, murder suspect identified
Police tracked him to Martinez and an 18-hour standoff ensued as he sat in a car near a gas station. Police took him into custody last Friday afternoon.