Castillo has been accused of hosting outings on his yacht in which the U.S. senator used the services of prostitutes. He has strongly denied the allegations and said he would seek a criminal investigation into the source of the reports.
On Monday, Castillo distributed copies of the woman's sworn statement to reporters during a press conference in his Santo Domingo office. The woman did not attend.
According to Castillo, the 23-year-old woman claims that she and a friend were approached by another Dominican lawyer, Melanio Figueroa, who was allegedly responsible for manufacturing the accusations against Menendez. The two women recited the accusations on a video that was recorded without their consent, he said.
Figueroa has not directly responded to numerous calls and emails seeking comment. Last month, an assistant at Figueroa's law office said they had dropped the case involving the two women on the video.
In Washington, Menendez told reporters that the accusations against him were "smears."
"I've always said that these are all false, they're smears, and so I look forward to seeing whatever the Dominican courts have that prove what I've said all along," Menendez said Monday.
Castillo, the son of a Dominican presidential adviser and the brother of a member of the country's Congress, has said he has known the U.S. senator for some 15 years and had never seen him with a prostitute. He said he's never hosted any parties involving prostitutes.
In the video released last year, the two Dominican women, whose faces were blurred, also claimed they had sex with Castillo and Dr. Salomon Melgen, a Florida eye doctor of Dominican descent who is a prominent Democratic campaign contributor and a major supporter of Menendez. De los Santos now claims that those allegations are also fabricated.
Menendez's ties to Melgen have come under close scrutiny after an FBI raid early last month at the doctor's West Palm Beach, Florida, offices. Menendez has acknowledged flying on Melgen's private jet to the Dominican Republic twice and was compelled to reimburse $58,000 for the two flights that he had previously failed to report.
A watchdog group called Citizens for Responsibility and Ethics in Washington, or CREW, has said it had received emails starting in April 2012 alleging that Menendez used the services of prostitutes in the Dominican Republic. The emails came from someone identified as "Peter Williams," though that may be a pseudonym.
Just before Menendez's successful re-election last November, The Daily Caller, a conservative web site, published a story that included a video interview with two women who claimed to be prostitutes. The women said Menendez paid them $100 for sex after agreeing to a fee of $500.
The Daily Caller did not immediately respond to emails and phone calls on Monday.
Associated Press writers Erica Werner and Henry C. Jackson contributed to this story from Washington.