Two Northland residents are potentially facing decades in prison if convicted of sexual assault and child pornography charges.

Matthew James Gunderson, 29, of Sturgeon Lake, and Amanda May Walsh, 37, of Aitkin, have each been ordered jailed without bail as they face charges in both federal and state courts. The two are or were in a relationship, according to court documents.

Authorities said the case involves at least two children, and a federal prosecutor indicated Tuesday that investigators believe there may be additional victims.

Court documents allege that Gunderson admitted to assaulting a preteen girl at a Carlton County hotel early this year. The victim was known to both Gunderson and Walsh, who was present at the time and allegedly aided and abetted the crime by "encouraging or directing" Gunderson, according to a criminal complaint.

Walsh is also accused of producing pornographic photographs of the same girl and sharing those images with Gunderson.

Details of the federal case remain sealed, but documents filed in State District Court in recent months offer some insight on the allegations.

The Aitkin County Sheriff's Office first began investigating the case in February, when a third party reported the discovery of suspected child pornography on a phone Walsh was known to use, according to court documents. Investigators found several nude images of the girl in various positions, authorities said, and it was discovered that Gunderson had sent numerous sexually explicit text messages to the victim.

In an interview, the victim told investigators that Walsh had forced her to pose naked while she took the photographs. Walsh then sent the photographs to Gunderson, the girl reported. In other communications, authorities said Gunderson sent the girl a nude photograph of a prepubescent boy.

The investigation led to evidence of the alleged sexual assault in Carlton County. Authorities said the incident occurred while Gunderson, Walsh and the girl stayed at Black Bear Casino Resort on the night of Jan. 31. Gunderson allegedly admitted to the assault after investigators executed a search warrant at his residence on March 1.

Assistant U.S. Attorney Laura Provinzino told the judge Tuesday that investigators have positively identified the girl and a boy who were victimized. Provinzino said images of two other young girls were also seized from devices belonging to Gunderson, but investigators had yet to positively identify the girls and determine whether the images were produced by the defendant.

Gunderson appeared Tuesday in U.S. District Court in Duluth as federal prosecutors took the uncommon step of appealing a bail decision. Magistrate Judge Leo Brisbois earlier this month ruled that Gunderson could be released from custody with supervision upon posting a $25,000 bond.

Chief Judge John Tunheim reversed that ruling, siding with prosecutors who contended that Gunderson would pose a substantial danger to the public if released, regardless of the conditions. Provinzino called the allegations "egregious" and noted that Gunderson could potentially spend the rest of his life in prison.

Gunderson and Walsh are each charged in federal court with production and distribution of child pornography. Convictions carry mandatory minimum sentences of 15 and 5 years, respectively. Prosecutors brought the charges by criminal complaint on June 26, and must convene a grand jury to seek a formal indictment within 30 days.

In State District Court, Gunderson is charged with first-degree criminal sexual conduct in Carlton County and is expected to face an additional count in Pine County, according to Provinzino. A conviction on that charge carries a presumptive sentence of 12 years in prison.

Walsh is charged in Carlton County with aiding and abetting first-degree criminal sexual conduct and in Aitkin County with production, possession and dissemination of child pornography.

Both are being held at the Douglas County Jail in Superior as they await future court appearances.