Clayton J. Courtney, 28, was charged Friday with first-degree intentional homicide. A court commissioner set his bond at $500,000.
Courtney already was charged with attempted first-degree intentional homicide, stemming from allegations that he stabbed his roommate in the shoulder and foot last month.
Courtney is now accused of killing Britney Cross and leaving her body behind a vacant building along the Rock River.
Police found several fist-sized rocks at the crime scene, and they believe one may have been used to kill Cross. One rock was found on her hair and was covered in what could have been blood, the criminal complaint said.
An autopsy revealed a "large amount" of dirt in her mouth and dirt and a small rock in her stomach, the complaint said. Authorities found dirt and some of her own hair stuffed into her pants, according to the complaint.
Prosecutors asked for a $1 million cash bond. Defense attorney Joshua Klaff called the amount "absolutely inappropriate" and sought a more modest amount.
Janesville police have been investigating Courtney since his May 4th arrest, after the roommate quoting Courtney as saying he'd killed three unnamed people that night.