Peterson's defense attorneys asked Judge Edward Burmila to issue a directed verdict of acquittal, saying the prosecution, which rested as court opened following three weeks of testimony, had not proven its case.
"They [the prosecution] have not conclusively established there was a homicide, or that the manner of death was homicide. In fact the evidence is there are differing opinions at this point," defense attorney Steve Greenberg said.
Burmila disagreed, the Chicago Tribune reported.
"If we distill down the state's case, the jury could find on these facts that the defendant was guilty of this offense," Burmila said. "The defendant's motion for a directed verdict is denied."
The trial now moves into the defense phase. Peterson is not expected to testify.
Peterson's attorneys say Savio died accidentally after falling in her bathtub and drowning in 2004. Prosecutors contend Peterson killed her after a bitter divorce, the Chicago Tribune said Monday.