Just over two weeks ago, in a highly publicised event, Troy Davis was executed by the state of Georgia despite global protest and significant evidence of his innocence. Since then, three other men have been executed by the states of Texas, Alabama and Florida, with little public outcry. All four were tortured by the United States government.

Monday being the 9th anniversary of the World Day Against the Death Penalty seems an appropriate moment to examine why I believe this.

According to the Convention Against Torture, a treaty ratified by the US in 1994, torture is defined, in part, as "any act by which severe pain or suffering, whether physical or mental, is inflicted on a person for such purposes as […] punishing him for an act he […] has committed or is suspected of having committed." The experience of American death row inmates fits this definition.

Among the approximately 3,250 prisoners on death row in the US, the vast majority will serve years in solitary and crippling conditions, awaiting execution. Of the 34 states that still kill people, at least 25 hold death row inmates in solitary confinement for 23 hours or more a day. Sensory deprivation is prevalent. On death row in Texas, hundreds of condemned men are isolated in 60-square-foot, single-person, solid-front cells for 23 hours a day. The prisoners exercise alone for one hour each day in a metal cage. Meals are served through a locking metal flap in the cell door. There are no work or group recreation programs; nor can the prisoners speak to each other through the solid cell walls and door.

Death row prisoners in the United States spend decades in these dehumanising conditions. Of the 52 people executed in the United States in 2009, the average length of time on death row was 169 months – over 14 years. Many spend much longer. Manuel Valle, for example, was executed last month by the state of Florida after 33 years on death row. Over those decades of lost time, it is not uncommon for prisoners repeatedly to come within hours of death, only to get a temporary reprieve, and then a new execution date.

While the details of Troy Davis's underlying prosecution became common knowledge to his legions of supporters, few knew that he had already come within minutes of execution before last month's 11th-hour ordeal. In 2008, Davis came within 90 minutes of execution – he was strapped down on the gurney when the US supreme court granted his stay. Later that year, he again came within three days of an execution date. In 2007, he came within a day.

Torture is a crime against humanity, a war crime and a violation of the Geneva conventions, as reflected in the statutes of the International Criminal Court, the international tribunal for the former Yugoslavia, and the international tribunal for Rwanda, among other judicial authorities. Over the last 15 years, a substantial body of law has developed that sets forth the elements of torture under customary international law, which largely reflects the definition of torture under the Convention Against Torture. Torture has been found to be "a violation of personal dignity and is used for such purposes as intimidation, degradation, humiliation and discrimination, punishment, control or destruction of a person".

Did anyone who closely followed Troy Davis's execution, and his temporary reprieve from the supreme court, doubt that the hours leading up to his execution – the hope and then betrayal – amounted to torture? Is there any meaningful difference between mock executions, long recognised as torture by the international community, and Davis's repeated last-minute temporary reprieves? Can we conceive of 30 years in a small gray cube, without access to another human being beyond mere sight of the hands of the guard who slides your food tray through a slot in your cell door, as anything but torture?