Updated

Police said Friday that they "expect" a 42-year-old convicted sex offender from Thailand will be charged in the murder of 12-year-old Zina Linnik, who police believe was kidnapped July 4 while watching a fireworks display.

Terapon Adhahn, who was convicted of incest in 1990, provided information that led to the discovery of the girl's body while being held for questioning, Tacoma Police Chief Don Ramsdell said. Adhahn, who lists a Parkland, Wash., address, was being held by federal immigration officials on a charge unrelated to Linnik's apparent abduction.

An autopsy was being conducted to determine Linnik's cause of death. Officials are also seeking a search warrant to obtain Adhahn's DNA.

“Our hearts and prayers are with the Linnik family and we will continue to put forth our best efforts to bring the perpetrator of this senseless and horrific crime to justice,” Ramsdell said at a brief and hastily arranged news conference Thursday night outside Tacoma Police Headquarters.

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Ramsdell said that Zina was found in a rural area “within Pierce County.” However, he declined to comment on the condition of the body when it was found.

Tacoma Police Detective Chris Taylor said the girl’s body was discovered at about 6 p.m. PDT, about the same time a meeting was taking place to organize a neighborhood search of Tacoma's Hilltop area, near the alley where the girl was last seen on July 4.

Police and FBI officials said Adhahn is a convicted sex offender and is charged with failing to register. He has denied having anything to do with the girl's disappearance.

Immigration and Customs Enforcement officials said Adhahn's 1990 conviction of first-degree incest is the basis for his detention, which should have led to the man’s deportation.

A search by FOXNews.com of the state's voter registration records shows that Adhahn registered in 2002, and his registration was current.

Court documents state he underwent court-ordered psychological evaluation and was diagnosed with pedophilia as part of the case, the Tacoma News Tribune reported.

The newspaper reported that investigators conducted a search of Adhahn's home on Sunday and Monday and removed items, including a gray van.

Witnesses reported seeing a gray van in the alley near Linnik's home immediately before she vanished.

Search warrant records also list “girl’s undergarments” removed from Adhahn's apartment, the newspaper reported.

Police reportedly located Adhahn by running a computer check of his van, and it matched the color and model, and the license plate number fit the partial description of a vehicle that Linnik’s father told police he saw driving out of the alley the night she disappeared, the newspaper reported. The father told police he heard a scream just before he saw the van speed away, police told the paper.

Adhahn told police his original plates had been stolen months earlier, and that the ones on his van were stolen. He came from Thailand to the United States in 1977 and later enlisted in the Army, the newspaper reported.

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The Associated Press contributed to this report.