The suspect, whom the woman described as a casual friend, was arrested Friday after he emerged from the woods following an all-night manhunt.
Scott J. Johnson, 38, was being held in jail Friday night to await an initial court appearance. He had not been formally charged in the shootings.
Authorities did not return calls seeking comment on whether the reported rape was related to the shootings. Jail officials did not know whether Johnson had an attorney.
The 24-year-old woman told The Associated Press in a phone interview Friday night that she met her attacker in December while shopping. The AP does not name people alleging sexual assault without their consent.
The woman said the two struck up a conversation and later bumped into each other occasionally in Kingsford, Mich. Kingsford and nearby Niagara are about 210 miles north of Milwaukee, along the Menominee River, which separates Wisconsin from Michigan's Upper Peninsula.
"We just became friends - not good friends, just friends," the woman said. "If he rode past on his bike, if he saw me working in the garden, he would stop and say hi."
On Wednesday evening, the man she knew only as "Scott" stopped and asked if she wanted to go for a bike ride, she said, then he led her down a remote road to a place he had taken her about a month earlier without incident.
"Scott told me that a lot of teenagers go down there, but I didn't know anything about that," she said.
The place was along the Menominee River, near a railroad bridge, which the two crossed to reach the Wisconsin shore.
When they went into the woods, the woman said, the man shoved her to the ground and raped her as she tried to fight him off. They later walked out of the woods and back across the bridge and to their bikes, then rode away, she said.
"I was trying to act as calm as I could," the woman said. "I didn't want to try to run away. Who knows what he would have done if I did?"
Police came to her home the next night. "They wanted me to describe what this guy looked like," she said.
By then, a massive manhunt was under way for the gunman in the riverbank shootings. More than 100 law enforcers from at least 10 agencies searched for him.
Johnson was dressed in camouflage when deputies confronted him the next morning. He dropped his assault rifle as officers approached.
Authorities in Wisconsin's Marinette County listed his address as Iron Mountain, Mich. But a protection order that the woman obtained Friday morning against Johnson said he lived in nearby Kingsford, about four blocks from her.