CLEVELAND, Tex.  The police investigation began shortly after Thanksgiving, when an elementary school student alerted a teacher to a lurid cellphone video that included one of her classmates.

The video led the police to an abandoned trailer, more evidence and, eventually, to a roundup over the last month of 18 young men and teenage boys on charges of participating in the gang rape of an 11-year-old girl in the abandoned trailer home, the authorities said.

Five suspects are students at Cleveland High School, including two members of the basketball team. Another is the 21-year-old son of a school board member. A few of the others have criminal records, from selling drugs to robbery and, in one case, manslaughter. The suspects range in age from middle schoolers to a 27-year-old.