Col. James Baker says Brooke Bennett's body was found in Randolph shortly before 5 p.m. and her family has been notified.
According to an affidavit, a 14-year-old witness has told investigators that Brooke's uncle brought Brooke to his home to initiate her into a child sex ring the day she disappeared.
She was last seen alive with the uncle, Michael Jacques, at a convenience store a week ago.
The 14-year-old told authorities she helped Michael Jacques take Brooke to Jacques' Randolph home on June 25 to be initiated into the ring. The 12-year-old has not been seen since then.
The 14-year-old girl, a relative of Jacques, said she understood that as part of the initiation, the 12-year-old "would have sex with adult males," according to the affidavit in U.S. District Court.
The girl said she and the 12-year-old watched television for a while before Jacques told her to leave and took the girl upstairs. The witness said she left the house with her boyfriend and did not see the girl again.
The 14-year-old said she herself had been sexually assaulted by Jacques, 42, since she was 9.
On Monday, Jacques, 42, was arraigned on an aggravated sexual assault charge involving a different girl, who is quoted in court papers as saying Jacques told her he would be her trainer in a "program for sex."
The girl said she had met three men in the program, including Jacques, and that she was told two other girls also were in the program. "The first who does it lives and the second gets her throat cut," she told police, according to an affidavit filed in court Monday.
Jacques dropped Brooke off at a convenience store on June 25, and surveillance video shows they left in separate directions. She had told family members she was going to meet a friend and visit a hospitalized relative of the friend but police believe that was a lie.
Jacques has 1993 convictions for kidnapping and aggravated sexual assault. Prosecutors argued against bail, saying he posed a threat to the accuser and had violated probation.
Earlier this week, the former stepfather of Brooke Bennet was arrested and authorities said Tuesday he would be charged with obstructing justice for destroying evidence.
Neither the FBI nor the head of state police discussed what evidence Ray Gagnon is alleged to have destroyed or whether that evidence was part of the investigation into Brooke Bennett's disappearance or unrelated sexual assault accusations against him.
Gagnon had been scheduled to be arraigned Tuesday on a sexual assault charge involving a minor but the arraignment was canceled as federal authorities took over. At an afternoon news conference, state police head Col. James Baker said that case was still being investigated and the charge could be refiled.
Brooke's father, James Bennett, who identified Gagnon as Brooke's stepfather, told CBS Early Show co-anchor Harry Smith on Tuesday, "I don't know what to think. There's been so much information out there, so many stories. All I can hope is that she's okay."
Bennett, who appeared via satellite link on The Early Show along side Brooke's emotional mother and sister, said the police were not giving them any more information than they were releasing to the media. "It's frustrating, but I understand why they can't give us the details."