Reporting from Denver — The advertisement appeared on Craigslist in early December.
"Need a real aggressive man with no concern for women," read the posting on the Internet classified advertising forum. Its purported author was a Casper, Wyo., woman, whose photo also was posted.
One week later, a man accepted the offer, forcing his way into the woman's home, tying her up and raping her at knifepoint.
"I'll show you aggressive," he allegedly said, according to court testimony.
In fact, authorities say, the woman had nothing to do with the ad. Instead, they say, a former boyfriend had posted it, soliciting her assault.
Such an incident would have been impossible -- or at least much less likely -- 20 years ago, Natrona County Dist. Atty. Mike Blonigen said. "It's probably only possible in our modern age," he said.
For Craigslist, the San Francisco-based website used by millions to sell and barter goods and services, the incident comes after a year punctuated by legal battles over its adult advertisements, as well as the highly publicized Boston slaying of a woman who advertised erotic services on the site.
Last year, Thomas Dart, the sheriff in Cook County, Ill., filed a federal lawsuit accusing the site of facilitating prostitution and urging the court to view it as a public nuisance. State attorneys general also pressured the company to eliminate what they called a "blatant Internet brothel."
Though Craigslist prevailed in the Illinois lawsuit, the website eliminated its erotic services section, replacing it with "adult services" and pledging to review every ad posted there to prevent flagrant prostitution and pornography.
Craigslist also has made headlines for cases of impersonation, including one last year in which a Long Island, N.Y., mother allegedly posted an ad seeking sex and directing men to the mother of her 9-year-old daughter's rival.
The Wyoming case began to unfold Dec. 5. Jebidiah James Stipe, 27, a Carbon, Wyo., native and Marine stationed at Twentynine Palms, Calif., allegedly posed as his ex-girlfriend and placed the ad seeking an aggressive man.
Two days later, she spotted it and contacted the Natrona County Sheriff's Office, as well as Craigslist, which took down the ad.
But Ty Oliver McDowell, 26, from Bar Nunn, Wyo., had allegedly already seen it.
McDowell, an employee of the Wyoming Medical Center's radiology department, e-mailed the address listed in the ad, according to an affidavit in the case.
McDowell later told authorities that he and the woman exchanged instant messages, and she described what she wanted -- "humiliation, physical abuse, sexual abuse," according to investigators -- and gave him her home address.
In fact, authorities say, McDowell was communicating with Stipe.
On Dec. 11, McDowell allegedly went to the woman's home and forced his way inside. He bound, blindfolded and gagged the 25-year-old woman, then raped her as he pressed a knife to her throat, the affidavit said.
Detectives said he told them he thought he was fulfilling her rape fantasy.
McDowell was arrested and charged with first-degree sexual assault, aggravated kidnapping and aggravated burglary. Stipe was also arrested and charged with conspiracy to commit first-degree sexual assault.
A maintenance mechanic who enlisted in the Marines in 2001, Stipe was in the process of being ejected for an undisclosed pattern of misconduct at the time of his arrest, a Marine Corps spokeswoman said.
Documents related to Stipe's arrest have been sealed. But as for the alleged rapist, Blonigen said his state of mind would be central to the case. Though jurors must weigh what McDowell believed to be true, they also must consider how a reasonable, objective person would view the situation, he said.
Blonigen said that although Craigslist officials had cooperated with the investigation, the fact that they published sexually suggestive ads also facilitated the crime.
"If I were king, I'd like to see them not run these personal ads," he said. "This is a debate we've had for a long time: . . . Do we censor the Internet?"
Craigslist did not respond to a request for comment.
Federal law protects Internet sites from liability for their users' actions, said M. Ryan Calo, residential fellow at Stanford Law School's Center for Internet and Society.
"The idea was that these website platforms were truly communities assembled of random users, with no editorial control over what users were doing. Craigslist is like a hotel with millions of rooms, but it doesn't have the ability to figure out what's happening in those rooms," Calo said.
A crime committed through a social networking site is no different than one perpetrated through a newspaper's printed classifieds, he said. Yet Internet-based crimes do make it easier for police to track down suspects because they leave a cyber-trail, Calo said.
But Steve Patterson, a spokesman for the Cook County sheriff who sued Craigslist, said the website wasn't blameless. By hosting an adult services forum, "they create this specific place for criminal activity to take place," he said.
As a "good corporate citizen," Craigslist should not involve itself in such business, he said.
Authorities have not said which section of the website published the posting, but Patterson noted that Craigslist had pledged to monitor adult ads.
He said it was unclear whether or how thoroughly it was doing so, and added that the Wyoming incident suggested a lack of monitoring.
"If a woman is putting an ad online saying she'd like to be raped, I'd hope it would be stopped," he said.
Correll writes for The Times.