Little is known about Sergio Martinez-Perez, who is accused of killing a 93-year-old Omaha woman and is in the United States illegally.
Martinez-Perez, 19, was formally charged Friday with first-degree murder in the rape and slaying of Louise Sollowin.
He is a native of Sonora, Mexico.
Shawn Neudauer, a spokesman for U.S. Immigration and Customs Enforcement, said Friday that federal authorities have placed a detainer on Martinez-Perez. That means that if Douglas County authorities were to release him, he would be placed in ICE custody.