Williams never saw the pornographic content in his Twitter feed, Jamerson said, and hadn't been aware that his account was following @RateMyLatin and @RateMyEbony until the Daily News raised the issue.
"A lot of people follow Seth and then will ask that he follow them, and then he'll just follow them" without investigating whom he's following, Jamerson said.
"That doesn't mean he's looking at what they're posting. . . . The only person he was following that he thought was scandalous was [comedian] Louis C.K."
(For those unfamiliar with Twitter, a user must click a "Follow" button to follow another account. A Twitter user can see the profile photo and description of the other account before clicking the "Follow" button.)
The profile photos for @RateMyLatin and @RateMyEbony - both of which feature busty, scantily clad women - would have popped up in Williams' Twitter feed every time the accounts tweeted.
Jamerson noted that Williams never retweeted any posts from the lewd accounts.
On Sunday, Jamerson said in an email that Williams had been a "victim of a phishing scam."
If the lewd accounts "tweet or retweet something that you write and you check to see who retweeted you or mentioned you in a tweet, you are automatically added to their followers," Jamerson wrote.
But Twitter denied that was possible.
"There's not a scenario through either our website or our mobile clients through which an @reply or retweet would cause you to automatically follow someone, intentionally or otherwise," Jim Prosser, Twitter's senior manager for communications, said in an email.
Williams seems to use his Twitter account - which clearly identifies him as the city's top prosecutor - daily. The account had 2,398 followers as of Tuesday evening.
The D.A. shares information about his office, retweets news stories and responds directly to questions and criticism from the public.
On several of Williams' more active tweeting days recently, @RateMyEbony and @RateMy Latin - which have more than 80,000 followers combined - also kept up a steady stream of tweets.
On March 4, for example, @RateMyEbony tweeted 16 photos, including one of a woman with her pants down, exposing a shapely backside. @RateMyLatin, meanwhile, tweeted 15 similarly salacious photos and links that day.
Williams posted 25 tweets throughout the day. None of the tweets referenced either of the lewd accounts.
Jamerson said Williams spent nearly three hours out of the office that afternoon to take his mother to the doctor's office and thus couldn't have seen any of the pornographic content.
Jamerson didn't respond when the Daily News asked if Williams could have viewed the lewd posts on his smartphone when he was out of the office.
She also suggested that someone else could have added the porn sites to Williams' account, noting that campaign staffers have used the account that bears his name and title.
Jamerson declined to answer further questions about campaigners' activity on Williams' account, saying city law forbids her from "any dealings with the political side of this."
Lisette Gonzalez, Williams' campaign manager, said none of Williams' passwords or login information has changed since campaign staffers created his Twitter and Facebook accounts in 2009.
"At least six different people had access to both accounts, and actively used those accounts on behalf of the D.A. if he was not able to post information due to his hectic schedule before and during taking office in 2010," Gonzalez said. "I do not know if those people still have access, because they are no longer with the campaign."
Gonzalez said she doesn't know the names of the now-departed staffers who had access to the account.
Jamerson said Williams' account will be "monitored more closely in the future so that this does not happen again."
The social-media policy for the D.A.'s office advises employees not to "engage in any online activity that . . . reasonably could be expected to negatively affect the Office's reputation or standing in the community or the criminal justice system."
The policy further notes that employees "are responsible for any of your online activity even if not using office equipment."
The Twitter snafu offers yet another reminder of the perils that social media pose to public officials.
"It just boggles my mind that the District Attorney's Office would have such a lax practice when it comes to login procedures," said Rob D'Ovidio, an associate professor of criminal justice at Drexel University who studies high-tech crime.
"As someone who oversees computer-crime prosecutions, they should have better computer security," he said.
"The bigger message here is: Change your password, and this is the reason why."
On Twitter: @dgambacorta