PORTLAND — A Lewiston man pleaded guilty Thursday in U.S. District Court to one count of sexual exploitation of a child.

By pleading guilty, Derek Hinkley, 30, admitted that he used his computer in summer 2012 to webstream images of a teenage boy masturbating. Hinkley threatened to cut off the boy’s genitals if he did not comply, according to the prosecution version of events to which he pleaded guilty.

Hinkley, also known as Ethan Hinkley, on July 18, 2012 used a knife to force two boys, aged 12 and 15, to follow his instructions, according to court documents. Images of the older teen, but not the younger boy, were streamed on the Internet.

The victims reported the incident to police the next day and Hinkley’s computers were seized, according to court documents. He was arrested by Lewiston police and indicted by the Androscoggin County grand jury on two counts of criminal threatening with a dangerous weapon.

The federal charge was filed in February 2013, according to the federal court’s website. Hinkley was indicted by a federal grand jury the following month.

Hinkley entered a conditional plea so that he can appeal U.S. District Judge Nancy Torresen’s denial of his motion to suppress statements made to the Lewiston police to the 1st U.S. Circuit Court of Appeals in Boston. Hinkley claimed he did not waive his Miranda rights. The judge, who will sentence him, disagreed.

The Lewiston man faces a mandatory minimum of 15 years and a maximum of 30 years in prison. He also could be ordered to pay a $250,000 fine.

Hinkley is scheduled to be sentenced in May.