SOUTH LAKE TAHOE, Calif. (AP) _ A man accused of sexually assaulting two young models and strangling their adult chaperones after posing as a filmmaker had held the girls captive in a soundproof box in a bedroom, investigators say.

Herbert James Coddington, 28, was being held without bail at the El Dorado County Jail today after arraignment Wednesday on capital murder charges and other offenses.

Coddington was arrested Monday after FBI agents burst into his trailer home, where they found the chaperones' bodies in plastic garbage bags and freed the terrified girls, ages 12 and 14, from an adjoining bedroom, the FBI said.

Investigators who asked not to be identified said the girls had been held without shackles in a large, box-like room-within-a-room soundproofed with scraps of rug. The box was secured, investigators said without elaborating.

Several firearms were found inside the trailer, located in a mobile home park, authorities said. Coddington lived alone, with neighbors close by.

District Attorney Ron Tepper, asked Wednesday about the reports, said only that authorities found a structure with soundproofing in the bedroom and that it was related to the crime.

Police said the girls had traveled here from Reno, Nev., with their chaperones, thinking they were going to take part in the making of an anti- drug video.

Coddington, appearing in court Wednesday in manacles, was arraigned on two counts of murder and several sexual offenses, including one count of rape, and a special allegation of multiple murder that carries the death penalty.

Federal kidnapping charges may be filed later, Tepper said. A preliminary hearing was set for June 4 on the state charges.

The girls' chaperones, Maybelle ''Mabs'' Martin, 69, operator of a Reno modeling school, and her companion Dorothy ''Dottie'' Walsh, 67, were slain Sunday, one day after they disappeared, the district attorney said.

FBI agent Terry Knowles said the models, Alecia Thoma, 14, of Reno, and Monica Berge, 12, of Sparks, probably were present when the women were slain.

Police believe Coddington, posing as a filmmaker, had canvassed at least four other modeling agencies for girls last week, using four aliases, said Reno Sgt. Greg Dion.

Teen-agers approached by a man believed to be Coddington gave a description of his expensive imported car, leading FBI agents to the mobile home, the FBI said.

After Coddington's arrest, officers dug under the trailer but found no evidence of any other human remains, Tepper said.

Authorities said they didn't know what Coddington's occupation was, adding that he apparently was unemployed for several years.

John Crow, manager of the trailer park, said Coddington claimed to be a writer working on a book. Neighbors said the man kept to himself.