"Our policy is that the site is run by the people who use it, and these people are happy to help us out," he said. "People do tend to prioritize. Users are more concerned with scams - but if they see something wrong, they will flag it."

"Things do come up that demand our attention," he said. "The police will contact us, and we respond much faster than other Web sites - the cops tell us that. We've also heard it from district attorneys across the country."

In some areas of the nation, where police aren't familiar with Internet law, Craigslist will help investigators better their understanding, Newmark said.

"We work with them to get them the evidence they need so the case they're working on won't get thrown out of court," he said. "It's better for the bad stuff to be on our site, and for us to respond to it, than for it to be on another site that might not act as quickly."

San Ramon police Chief Scott Holder said his department checks Craigslist - and other sites - on a weekly basis. In three months, the department has conducted three sting operations as a result of online postings.

In Danville, prostitution is less of a problem. Police Chief Chris Wenzel said his department will occasionally check out Craigslist "if we hear certain things."

"(Other towns) have certain buildings - hotels and apartment complexes - that make prostitution easy," Wenzel said. "We don't really have that much of a problem with it, though it is always a concern."

Generally, word of women selling sexual favors reaches the department through the grapevine, Wenzel said, noting police raided a Danville establishment engaging in risky business six months ago.

"We monitor Craigslist and other potential sources, but we don't do it daily," Krull said. "In terms of whether prostitution is a problem in Livermore, we receive very few complaints. From that, I'd conclude it's not much of an issue."

That said, Krull acknowledged there were "several still-active investigations" into illegal sex activity in Livermore. Whether the operations are the result of information derived from Craigslist or other Web sites, Krull would not say.

In the meantime, Craigslist's Newmark said he will continue to assist law enforcement when called upon but will not eliminate the "erotic services" section of the Web site.

"The primary purpose of that category is so that these kind of postings can go there as opposed to being listed in the mainstream sections," he said. "We have discussed getting rid of the category, but we concluded that would make the problem worse."

Striking a sympathetic tone, Newmark said that although he sometimes sees postings that make him "wince," he believes people need to "practice compassion for those who author these ads."

"Everybody has an opinion, and everybody has a chance to express it," he said. "Free speech and compassion trump my personal reactions. Give someone a break - that's an important message."

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