Speaking to Al Jazeera from Berlin, Henning Riecke, from the German Council on Foreign Relations, said: "The prosecution, first on the civilian side and then on the military side, looked whether the colonel had broken law.
"Whether he had done a breach of international law, of martial law, or whether he had done a breach of public service law in the sense that he worked against the regulations within Nato and the Bundeswehr (German army).
"Both prosecutions have been terminated because there has not been an evidence for such a breach, but this does of course not mean that the act itself, which was possibly an error under imperfect information, did not a cause a tragic consequences.
"So the legal part of it is over but the political ramifications might last on."
A Nato fact-finding team estimated a day after the bombing that about 125 people had been killed and that at least 24, but perhaps many more, of those killed had been civilians gathering fuel from the tankers.
Klein has said that he called in the attack because he feared the tankers could be used in an attack on a nearby German military base.
|Germany's defence minister called the strike 'militarily inappropriate' [EPA]
Later investigations, including one carried out by German officials, gave varying figures for civilian casualties from at least 83 killed to more than 100.
The German defence ministry said last week it had paid out $430,000 to the 86 families of 102 Afghans killed or injured in the air raid, saying the money was intended "not as compensation in the legal sense but ... [as] humanitarian assistance".
Germany's defence minister at the time of the incident resigned, while the armed forces chief of staff and another senior defence official quit after pressure from Karl-Theodor zu Guttenberg, the minister's successor, who called the strike "militarily inappropriate".
Germany is the third-largest contributor of foreign troops in Afghanistan after the US and Britain, with around 4,500 soldiers in the relatively peaceful north.
Forty-three soldiers have died since the beginning of operations and polls suggest a majority of Germans are opposed to the Afghan mission.