Laci Peterson's (search) parents now want to exact an even pricier revenge on their killer son-in-law — to the tune of $25 million.

Sharon Rocha (search) and her husband, Ron Grantski, amended their $5 million wrongful-death suit against Scott Peterson this week, arguing that a larger judgment against him "would send a message . . . that such vicious and outrageous savagery inflicted by one human being shall be met with the severest of civil penalties."

The new suit amends one that they filed in 2003, a year after Laci was murdered in Modesto.

In addition to the increase in damages asked, it also adds as a plaintiff Dennis Rocha, Laci's father, who divorced Sharon in 1976.

The suit's purpose is to prevent Peterson from making megabucks on a book or movie deal, lawyers for Laci's family said.

The high-profile case has already led to several best-selling books, including one by his mistress, Amber Frey.

Geragos would not comment Wednesday on his request for funds. The lawyer has refused to say how much he was paid.