It's 2050. Humans have mastered commercial space travel. Hundreds of people pay thousands of dollars to be sent into orbit in a spaceship. Maybe some decide to help colonize Mars.
Then, trouble. A jilted spouse. A smuggled firearm. Perhaps a struggle followed by suffocation. A space traveler is found dead on board a ship or on the Red Planet. Who has jurisdiction over such crimes? Is there such a thing as a cosmic Hercule Poirot? Could someone fall through the cracks and get away with space murder?
To date, no one has been victim of a space crime. But because no one nation can lay claim to ownership of space, the idea of a criminal offense committed outside of our atmosphere is something people have already given some thought to.
According to NASA engineer and instructor Robert Frost, the language of law for galactic felonies would be the Outer Space Treaty of 1967. In Article VIII of the treaty, nations engaging in space exploration agree that they will bear responsibility for the actions of personnel aboard their craft. In other words, if a privatized shuttle from China sees a fight break out among crew members, leaving one injured, China would be the entity responsible for handling legal repercussions.
That varies slightly with the International Space Station, or ISS, which is home to a number of personnel from different nations. In the case of the ISS, an intergovernmental agreement signed in 1998 mandates that the home country of the offender will handle any investigation or prosecution. If the victim is a national of another country, that country will have the right to inquire as to the criminal status of the offender and seek to have jurisdiction over the matter if they feel justice isn't being meted out.
In most cases, space crime sprees would be treated the same as if an offender was traveling in a foreign country or in international waters. If you're a U.S. citizen and decide to bludgeon someone at sea or on the Moon, the various international agreements and national laws would determine how you get prosecuted. (Assuming, of course, you returned to Earth to answer the charges.)
Space crimes pose another intriguing wrinkle. In terra firma investigations, authorities can secure crime scenes, question witnesses, and preserve evidence. Aboard a spaceship or on a distant planet, these procedures would be difficult to perform, and almost impossible to do in a timely fashion. Even if a criminal investigator is on Mars, low gravity will affect blood spatter and bodies may even decay at a different rate than they do on Earth. While an American may be found liable for murder, proving it was malicious and not the result of the dangerous environment would give any prosecutor a headache. A defense attorney, on the other hand, would have a field day questioning defective spacesuits or toxic exposure to strange space chemicals.
Then again, prosecutors may not have to concern themselves with evidence. Thanks to airlocks and restrictive suits, the movement of space travelers is highly monitored. It would be hard to make any plausible deniability about one's whereabouts.
The closest thing to space crime that law enforcement has yet encountered may be crimes committed in Antarctica, the frigid and isolated continent that's unaffiliated with any country but operates under the Antarctic Treaty signed by 54 nations. The agreement declares that the suspect is likely under their home country's jurisdiction. In some cases, the country owning the research station where the alleged crime took place steps in. In 2018, a Russian researcher at Bellingshausen Station on King George Island went after his victim with a knife in the station's dining room. He was charged in Russia, though reports indicate the case has since been dropped. And in 2000, an Australian astrophysicist suspected of being fatally poisoned had an autopsy performed in New Zealand. The exam showed he had ingested methanol, but it remains unknown whether he did so accidentally or whether someone gave it to him. New Zealand police were unable to determine the source.
A person committing murder in space would certainly be held responsible. But whether they'd ever be found guilty beyond a reasonable doubt remains very much up in—and beyond—the air.