Wesley Brownlee, 43, had already been charged with three counts of first-degree murder after he allegedly went on a murder rampage in the Central Valley, hunting victims at random while masked and clad in black.
Prosecutors in San Joaquin County filed an amended criminal complaint this week charging Mr Brownlee with the murders of Juan Alexander Vasquez, Mervin Harmon, Paul Yaw and Salvador Debudey Jr., as well as the attempted murder of Natasha LaTour.
Three of the four murders had already been publicly linked to Mr Brownlee, but charges had not yet been filed.
A fourth, previously unreported case stems from the April 2021 slaying of Juan Alexander Vazquez.
Mr Brownlee was already charged with the first-degree murder of three men in Stockton: Jonathan Rodriguez Hernandez, who died on 30 August, Juan Carlos Carranza-Cruz, who died 21 September, and Lawrence Lopez, who died on 27 September.
Yaw was killed on 8 July, Debudey on 11 August, both in Stockton. Hermon and Vasquez were killed in Alameda County in April 2021.
Prior to his arrest on 15 October, the spree of killings committed under the cover of darkness had left city residents on edge.
Stockton Police Chief Stanley McFadden said at the time that the suspect had been apprehended at 2am after his car was stopped by a surveillance team in the Village Green Drive area of the city.
He was carrying a firearm and had a mask round his neck, and “was out looking to kill, he was hunting,” Mr McFadden told reporters.
Police had released grainy images of a suspect, and only had a partial description from Ms LaTour, who was also shot in April 2021, and is the only victim who is known to have survived.
Mr Brownlee spent several years in prison for separate drug offenses in the late ‘90s and early 2000s, and was banned from owning a gun, police said at the time of his arrest.
He allegedly used an unregistered “ghost gun” to carry out at least some of the slayings, police said in October.
Mr Brownlee is scheduled to appear in court on 3 January for an arraignment, prosecutors said in a statement.