SIOUX CITY – A Guatemalan child rapist who illegally returned to the United States, lived in Northwest Iowa without registering as a sex offender and was discovered after an OWI-and-eluding arrest is headed to federal prison.
Sergio Niz-Mendez, 27, formerly living in Sheldon, was sentenced Thursday, August 6, 2026, to 16 months in federal prison.
Niz-Mendez pleaded guilty March 23 to illegal reentry under 8 U.S.C. § 1326(a) and failure to register as a sex offender under 18 U.S.C. § 2250(a).
Federal prosecutors said Niz-Mendez is a Guatemalan citizen who was convicted in Massachusetts in 2016 of rape of a child with force for an offense committed when he was 15 years old. He served prison time and was removed from the United States in 2018.
Niz-Mendez later returned without receiving permission from the federal government and settled in Sheldon. Despite his qualifying sex-crime conviction, he failed to register as a sex offender while living in Iowa.
Authorities found him in O’Brien County in December 2025 after his arrest for operating while intoxicated and eluding. That Iowa prosecution is identified in federal records as case number OWCR013724.
U.S. District Court Judge Leonard T. Strand imposed concurrent 16-month prison terms for the two federal convictions. The sentence must be served consecutively to any incarceration imposed in the pending O’Brien County case or the related Massachusetts matter.
Niz-Mendez must serve five years of supervised release after leaving prison. Conditions prohibit him from knowingly contacting children younger than 18 or visiting places where children live or gather without prior approval from federal probation officers.
He must also complete a mental-health evaluation that may include sex-offender treatment, undergo a substance-abuse evaluation and testing, refrain from possessing or consuming alcohol and stay out of bars and taverns unless probation officers approve.
If Niz-Mendez is removed from the United States, he cannot legally return without permission from the secretary of Homeland Security. If he reenters during the supervision period, he must report to the nearest federal probation office within 72 hours.
The court imposed a $200 assessment but no fine or restitution. There is no parole in the federal prison system.
Niz-Mendez remains in United States Marshals Service custody pending transportation to a federal prison. The federal prosecution was filed as case number 5:25-cr-04065.
NIT previously reported a strikingly similar case involving a deported Guatemalan sex offender and drunk driver caught living illegally in Northern Iowa.
The Niz-Mendez case was prosecuted under Operation Take Back America, a nationwide Department of Justice initiative targeting illegal immigration, cartels, transnational criminal organizations and violent offenders.
Assistant U.S. Attorneys Patrick T. Greenwood and Shawn S. Wehde prosecuted the case. The Department of Homeland Security conducted the investigation.