Otto Warmbier was a 21-year-old University of Virginia economics major with a bright future when he signed on for a short tourist trip to North Korea in December 2015. Not until Tuesday was he finally flown home to Cincinnati, gravely ill and reportedly in a coma.

He was arrested, tried on spurious charges and evidently subjected to horrendous mistreatment by North Korean authorities. This was outrageous behavior even by the standards of one of the world’s most vicious and isolated regimes. It should not go unpunished.

By his account, delivered at a scripted “news conference” weeks after his arrest, Warmbier attempted a foolish but harmless prank: trying (unsuccessfully) to pilfer a propaganda poster from the hotel where he was staying. For this he was sentenced to 15 years hard labor on a charge of “hostile acts against the state” following a one-hour trial in March 2016. He had not been seen in public since then. Now it appears that Warmbier may have been gravely ill for much or all of that time.

The harm done to an innocent student is the result of North Korea’s odious practice of seizing Americans to use as political pawns. Three other U.S. citizens are being held by the regime; President Trump should make their release a priority.

The United States should also move quickly to step up sanctions on the regime of Kim Jong Un, which has been racing to develop missiles that can reach the United States with a nuclear warhead. A new report by the research group C4ADS shows that by cracking down on a relatively small number of interlinked Chinese companies and individuals, the pressure on Pyongyang could be greatly increased.

The Trump administration has asked China to act against some 10 entities; if Beijing does not respond promptly, the United States should act unilaterally.