Grasso filed court papers Thursday claiming prosecutors didn't meet the evidentiary standards to prosecute the former football star on six of the 12 charges against him.
"They're charging O.J. with ... the specific intent to commit robbery," Grasso said, citing Nevada law underlying the felony charge of robbery. "He wasn't stealing from somebody else. He was taking back something that was his."
Simpson, 60, is accused of leading five other men in the gunpoint robbery of two memorabilia dealers who were peddling collectibles associated with Simpson, including the suit he wore the day he was acquitted in the murders of his ex-wife, Nicole Brown Simpson, and her friend Ron Goldman.
Simpson has denied any knowledge of guns being involved in the confrontation. He has said he intended only to retrieve items that had been stolen from him by a former agent.
"Simpson's indisputable sole intent to retrieve his own property negates the crime of robbery as charged," Grasso said in Thursday's court filing. He also contended that "the crime of kidnapping was not shown to exist to the slight or marginal extent required under Nevada law."
Grasso said Simpson would fight the other six charges against him at his trial, set to begin April 7. Those counts include burglary, coercion and assault with a deadly weapon.
A spokesman for Clark County District Attorney David Roger wouldn't comment Friday.
District Judge Jackie Glass has set a Feb. 21 deadline for prosecutors to respond and a March 7 hearing on motions in the case.
Charles Ehrlich, Clarence Stewart are being tried with Simpson; three former co-defendants have pleaded guilty.
Stewart and Ehrlich have also challenged some of the charges and Ehrlich's attorneys have asked the judge to separate his trial from Simpson's.
Simpson, Stewart and Ehrlich are all free on bond after pleading not guilty to all charges.
