Steven M. Zelich, 52, a former West Allis police officer, was arrested Wednesday.
The bodies were found by road workers in rural Geneva, Wis., in early June. Both women had been dismembered.
One has been identified as Laura Simonson, 37, of Farmington, Minn. She was reported missing in November.
The identity of the other woman remains unknown, Police Chief Steven Hurley said.
Zelich, a licensed security guard, was an independent contractor for a website called Legal Shield that offers advice on issues like real estate transactions and traffic citations. Investigators said the also posted on a discussion board, "MasterB Slave Club."
In one posting, Zelich or someone who appeared to be him sought a candidate for "no limit enslavement, imprisonment, captivity, animalization."
Simonson's father told the Milwaukee Journal Sentinel that his daughter, who had seven children, had a history of mental illness and had advertised as an escort on CraigsList. In a telephone interview, Richard Wierson said he is now caring for his grandchildren.