(CNN) -- The man that prosecutors say is behind the stabbing deaths of four homeless men in Southern California now stands accused of the brutal killing of a mother and brother of an old friend, authorities said.
The latest allegations against Itzcoatl Ocampo, 23, were made public Friday, shortly after authorities dropped charges against the friend, Eder Herrera, in the killings.
Ocampo will be arraigned Monday on charges he stabbed to death 53-year-old Raquel Estrada and her 34-year-old son, Juan Herrera, Orange County District Attorney Tony Rackauckas told reporters.
"This case has expanded from murdering random, vulnerable strangers to murdering people he knew," he said.
Authorities say Estrada was stabbed more than 30 times and Herrera more than 60 times on October 25, their bodies left in pools of blood inside their Yorba Linda home.
Herrera, 24, was arrested a day later in large part because of eyewitness statements and surveillance video from a nearby store that showed someone resembling Herrera in the area at the time of the killings, Rackauckas said.
But the brutality and similarity of the attacks caught the attention of a law enforcement task force created to investigate the homeless killings.
It is the latest twist in the case that began on December 20 when the body of a homeless man who had been stabbed more than 40 times turned up in Orange County.
Herrera and Ocampo, an Iraq war veteran, had been friends since their high school days, Rackauckas said. The two lived about a mile apart, he said.
The district attorney did not comment on a possible motive in the murders of Estrada and her son.
While charges against Herrera were dropped, he remained in custody at the Orange County jail late Friday on an immigration hold, authorities said.
Ocampo has been in custody since his January 13 arrest on suspicion of killing 64-year-old John Berry outside a Carl's Jr. in Anaheim, authorities said. His arraignment in the homeless killings has been postponed until February 17.
Ocampo is also accused of killing James McGillivray, 50, who was killed December 20; Lloyd "Jimmy" Middaugh, 42, who died December 27 and Paulus "Dutch" Smit, 57, killed on December 30.
Ocampo served in the Marines from July 2006 until July 2010, and was deployed to Iraq for six months in 2008, according to Marine service records. He completed his service, with the rank of corporal, with the 1st Marine Logistics Group at Camp Pendleton, south of Orange County.
CNN's Greg Morrison and Rosalina Nieves contributed to this report.