"They are trying to deny my client the right to the counsel of his choosing," Kusturiss said. He said Poole was not part of Ingle's defense.
Assistant District Attorney Thomas F. Lawrie declined to comment on the petition.
Ingle's father, a Boeing Co. engineer, had planned to fake his own death, run off with his Russian mistress and a fake passport, and leave $3.6 million in life insurance for his family. Investigators said he likely knew his killer.
Parth Ingle received two years' probation in November for steps he took to pry into his father's e-mails.
This is not the first time prosecutors have tried to bar Kusturiss from defending him. The same issues were raised in his first trial, but County Court Judge Ann A. Osborne ruled that Kusturiss could continue.
In that case, John Kusturiss questioned both his son and his son-in-law - the latter a federal investigator whom Parth Ingle contacted after learning that his father was seeking a fake passport.
An exhibit in Wednesday's filing by prosecutors detailed a state trooper's 2008 interview with Gordon Kusturiss, who was at college at the time of the slaying. He told police that Parth Ingle feared for his own safety and that of his mother and sister, and that he was afraid his father would "have them killed and collect the insurance policies."
A preliminary hearing in the case was postponed. A hearing on the motion has not been scheduled.
Contact staff writer Mari A. Schaefer at 610-892-9149, firstname.lastname@example.org or @MariSchaefer on Twitter.