Costa was originally charged with reckless driving and vehicular manslaughter.
An L.A. County grand jury returned an indictment last week that was unsealed Friday. Now the District Attorney's office says investigators presented the jury with additional information in this case, which led them to the two new murder charges against the driver.
Two counts of murder were added in an indictment last week that also alleged vehicular manslaughter and reckless driving causing injury. Angel Posca, 58, and his daughter Angelina, 12, were killed in the crash on April 1 when their car was struck by the truck which had lost its brakes and careened down Angeles Crest Highway.
The rig pushed the car about 200 yards into the intersection of Foothill Blvd., where four other vehicles were struck, before the truck smashed into a coffee shop and a book store. A dozen other people were injured.
Costa's attorney accuses the D.A. of confusing tragedy with a crime.
"Just because someone tragically dies, it's not a murder," said attorney Steve Meister. "And this case isn't a murder, it never was. It's an inappropriate, excessive charge, and we're going to fight it very dedicatedly."
Costa had been free on $200,000 bail. He was rearrested Friday and now his bail has increased to $2 million.
"When you bring murder charges in a case that shouldn't be charged as a criminal case at all, it stops being a prosecution, it starts being a lynch mob," said Meister.
Costa is from the Boston area. He will appear in Pasadena Superior Court next Wednesday for a bail review hearing. If convicted on these charges, he faces life in prison.