Did the FBI execute Ibragim Todashev? He appears to have been shot seven times while being interviewed at home in Orlando, Florida, about his connection to one of the Boston bombing suspects. Among the shots was the assassin's hallmark: a bullet to the back of the head. What kind of an interview was it?

An irregular one. There was no lawyer present. It was not recorded. By the time Todashev was shot, he had apparently been interrogated by three agents for five hours. And then? Who knows? First, we were told, he lunged at them with a knife. How he acquired it, five hours into a police interview, was not explained. How he posed such a threat while recovering from a knee operation also remains perplexing.

At first he drew the knife while being interviewed. Then he acquired it during a break from the interview. Then it ceased to be a knife and became a sword, then a pipe, then a metal pole, then a broomstick, then a table, then a chair. In one account all the agents were in the room at the time of the attack; in another, all but one had mysteriously departed, leaving the remaining officer to face his assailant alone.

If – and it remains a big if – this was an extrajudicial execution, it was one of hundreds commissioned by US agencies since Barack Obama first took office. The difference in this case is that it took place on American soil. Elsewhere, suspects are bumped off without even the right to the lawyerless interview Ibragim Todashev was given.

In his speech two days after Todashev was killed, President Obama maintained that "our commitment to constitutional principles has weathered every war". But he failed to explain which constitutional principles permit him to authorise the killing of people in nations with which the US is not at war. When his attorney general, Eric Holder, tried to do so last year, he got himself into a terrible mess, ending with the extraordinary claim that "'due process' and 'judicial process' are not one and the same … the constitution guarantees due process, not judicial process". So what is due process if it doesn't involve the courts? Whatever the president says it is?

Er, yes. In the same speech Obama admitted for the first time that four American citizens have been killed by US drone strikes in other countries. In the next sentence, he said: "I do not believe it would be constitutional for the government to target and kill any US citizen – with a drone, or a shotgun – without due process." This suggests he believes that the legal rights of those four people had been respected before they were killed.

Given that they might not even have known that they were accused of the alleged crimes for which they were executed, that they had no opportunities to contest the charges, let alone be granted judge or jury, this suggests that the former law professor's interpretation of constitutional rights is somewhat elastic. If Obama and his nameless advisers say someone is a terrorist, he stands convicted and can be put to death.

Left hanging in his speech is the implication that non-US citizens may be killed without even the pretence of due process. The many hundreds killed by drone strikes (who, civilian or combatant, retrospectively become terrorists by virtue of having been killed in a US anti-terrorism operation) are afforded no rights even in principle.

As the process of decision-making remains secret, as the US government refuses even to acknowledge – let alone to document or investigate – the killing by its drones of people who patently had nothing to do with terrorism or any other known crime, miscarriages of justice are not just a risk emerging from the deployment of the president's kill list. They are an inevitable outcome. Under the Obama doctrine, innocent until proved guilty has mutated to innocent until proved dead.

The president made his rejection of habeas corpus and his assumption of a godlike capacity for judgment explicit later in the speech, while discussing another matter. How, he wondered, should the US deal with detainees in Guantánamo Bay "who we know have participated in dangerous plots or attacks, but who cannot be prosecuted – for example because the evidence against them has been compromised or is inadmissible in a court of law"? If the evidence has been compromised or is inadmissible, how can he know that they have participated? He can suspect, he can allege, but he cannot know until his suspicion has been tested in a court of law.

Global powers have an antisocial habit of bringing their work back home. The British government imported some of the methods it used against its colonial subjects to suppress domestic protests and strikes. Once an administrative class becomes accustomed to treating foreigners as if they have no rights, and once the domestic population broadly accepts their justifications, it is almost inevitable that the habit migrates from one arena into another. If hundreds of people living abroad can be executed by American agents on no more than suspicion, should we be surprised if residents of the United States began to be treated the same way?

• A fully referenced version of this article can be found at monbiot.comTwitter: @GeorgeMonbiot