Appealing to terrorists' sense of humanity and decency is a lost cause, a new study suggests.
That's because they are overwhelmingly focused on outcomes, and don't care about the collateral damage, South American researchers have found.
Sandra Baez of Favaloro University in Argentina interviewed 66 Colombian right-wing paramilitaries in jail for terrorism. Between them, they'd killed more than 2000 people. Her team also spoke to 66 non-criminals and 13 murderers.
All the participants underwent psychological and cognitive testing.
What they found was compared to normal people, "moral judgement in terrorists is abnormally guided by outcomes rather than by the integration of intentions and outcomes".
In other words, a "terrorist's moral code prioritises ends over means" the study, published in Nature Human Behaviour, concludes.
"Moral judgement was the measure that best discriminated between terrorists and non-criminals."
They also found - perhaps not surprisingly - terrorists have higher levels of aggression and are less likely to recognise the emotional impact of violent actions.
No link was found between each terrorists' intelligence and their inability to feel empathy.