Once you've been found guilty of a crime, can the government just assert that you're guilty of new crimes without having to prove it to a jury beyond a reasonable doubt?
No. A plurality of the U.S. Supreme Court recently upheld the basic right to a jury trial when you're being accused of a new crime. The government cannot simply impose new punishments on parolees without empaneling a jury of their peers and requiring the prosecution to prove their guilt beyond a reasonable doubt.
The case involved a man who had been convicted of possessing child pornography. Two years into a 10-year supervised release term, parole officers performed a surprise search of the man's apartment and allegedly found new child pornography. Without a new trial, a judge imposed a mandatory minimum sentence of five years.
The man appealed, and the 10th Circuit Court of Appeals found that the federal statute authorizing the additional sentence was unconstitutional because it "imposes heightened punishment on sex offenders based, not on their original crimes of conviction, but on new conduct for which they have not been convicted by a jury beyond a reasonable doubt."
Does this mean parole violations can't be punished?
Not at all. When a defendant is on parole or supervised release, violating the conditions results in a return to prison to serve the original sentence. The ruling only means that courts may not impose additional prison time without due process.
In other words, it was reasonable to punish the defendant for his supervised release violation, but the punishment could not constitutionally exceed his original sentence unless new charges were formally brought and a jury trial was offered.
Justice Neil Gorsuch wrote the opinion, joined by justices Ruth Bader Ginsburg, Elena Kagan and Sonia Sotomayor. Justice Stephen Breyer didn't officially join the opinion but concurred with it.
Gorsuch wrote that, "we do not hesitate to hold that the statute violates the Fifth and Sixth Amendments."
Justice Samuel Alito, however, sharply dissented from the ruling, notably asserting that the plurality's opinion "sports rhetoric with potentially revolutionary implications." Chief Justice John Roberts and justices Clarence Thomas and Brett Kavanaugh joined the dissent.
This case is crucially important because it requires the government to prove your guilt before a jury and beyond a reasonable doubt every time it seeks to take your liberty.
One can easily imagine a situation in which a bad actor could baselessly accuse a parolee of a new crime and get that parolee punished with additional prison time. A jury trial with a reasonable doubt standard is essential to prevent governments from endlessly tacking on additional sentences based merely on a parole officer's allegations.