OREGON CITY, Ore. - A 15-year-old Texas girl found strangled in a Milwaukie apartment last month was killed during the course of an attempted rape, prosecutors said Tuesday.

The revelations came as the men charged in connection with her murder made their first appearance in a Clackamas County court on Tuesday.

On Wednesday, federal officials also confirmed the pair said they were in the country illegally. Lorie Dankers, a spokeswoman with federal Immigration and Customs Enforcement, said both admitted to crossing into the U.S. illegally from Mexico some six months ago.

Cousins Alejandro Emeterio "Alex" Rivera-Gamboa, 24, and 23-year-old Gilberto Javier Arellano-Gamboa have both been charged with aggravated murder in the death of Dani "D.J." Countryman of Kaufman, Texas.

Her body was found July 28 in an apartment at the Balboa Apartment Complex at 2717 S.E. Courtney Road, where Countryman and her older sister, Ashley, had gone to a party the night before.

Ashley found Dani dead when she went to check on her. The 15-year-old was on a mattress in a back bedroom, and two other people were sleeping just a few feet from her.

According to a statement of probable cause filed by the Clackamas County Sheriff's Department, Alejandro Rivera-Gamboa told police during an Aug. 6 interview that he awoke the night of the party in apartment No. 19 to find his cousin, Gilberto Arellano-Gamboa, on the floor on top of Dani.

"The girl had been struggling and Arellano asked Rivera for help," the court document said. "Mr. Rivera admitted that he had held her down with his foot on her throat until she stopped moving."

A shoe seized from Rivera-Gamboa was found to have blood on it, and the pattern on the shoe was consistent with the imprint pattern found on Dani Countryman's chest, the document said.

Gilberto Arellano-Gamboa told police he did not remember his cousin killing Dani Countryman, according to the document.

The pair were in Clackamas County court for just a few minutes Tuesday, long enough for a judge to deny bail. A preliminary hearing is set for next week.

Court proceedings for the murder charges will need to be completed before authorities can turn their attention to the illegal residency issues. There is an immigration hold on the pair.