Donetsk: At first glance, the prisoner swap between the Ukrainian government and pro-Russian separatists appeared fair enough: on a deserted stretch of highway along the front line, each side released 28 captives, observing a principle of numerical parity.

Under the watchful eyes of mediators from the Organisation for Security and Co-operation in Europe, the prisoners walked past one another to freedom.

Motley crew: Pro-Russian prisoners-of-war walk along a road as they wait to be exchanged near Donetsk. Credit:Reuters

Then the questions started to pop up. The pro-Russian separatists – who, with the aid of the Russian army, routed the Ukrainians in battles in August, taking many captives – released men appearing to be actual prisoners of war.

The Ukrainians, however, widely understood to be lacking enough prisoners of their own to effect a one-for-one exchange, set free a motley group of men, women and teenagers wearing tracksuits or dirty jeans, and taken, they said, from jails as far away as Kiev.