Brodsky said Thursday's arrest of Peterson in the death of his third wife, Kathleen Savio, was likely the result of political pressure, the Chicago Sun-Times reported.
"I think the state's attorney has been under tremendous political pressure to bring a charge," Brodsky said in an appearance on CBS's "The Early Show" Friday.
Peterson, a former Bolingbrook, Ill., police sergeant, was charged with killing Savio, whose 2004 death was previously ruled an accidental drowning. His arraignment in Will County Circuit Court in Joliet, Ill., had been scheduled for Friday but was postponed until May 18, the Chicago Tribune reported.
Brodsky told "Good Morning America" his client previously had passed a lie detector test in Savio's death.
"He passed that polygraph exam 100 percent," Brodsky said.
Peterson, 55, is also suspected in the disappearance of his fourth wife, Stacy, 23, who vanished in October 2007 and is thought to be a potential homicide victim. Peterson maintains she ran off with another man.