The families of three of the victims, Dean Finocchiaro, Thomas Meo and Jimi Patrick, filed the civil suit on Monday.
Their attorneys say that due to DiNardo's documented mental health issues, his parents should have prevented his access to guns and the company-owned construction equipment used in the murders.
The bodies of the victims were found at the family's Solebury Township farm in July 2017.
Authorities said in court documents that DiNardo said he lured the four men to the sprawling farm owned by his parents under the guise of marijuana transactions before killing them there. All four were shot and three were set on fire and placed in an oil drum that was buried.
"Had he not had access to the gun, the backhoe, the pig roaster and the farm itself, this crime could not have been committed," said Thomas Kline, the Finocchario family attorney.
A lawyer representing Antonio and Sandra DiNardo was out of the country and unavailable for comment, the Associated Press reports.
During the news conference in Center City, we also heard from the families of those three young murder victims.
It was the first time that some of the distraught relatives spoke publicly about their loss.
"We miss Jimi every day," said Patrick's grandmother, Sharon. "There isn't a day that goes by that I don't cry when I think of Jimi."
DiNardo and co-defendant Sean Kratz have pleaded not guilty in the case. They are also named in a previous wrongful death lawsuit filed by Sturgis' family.
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