Faisal bin Ali Jaber, brother-in-law and uncle respectively to the two men killed in the attack, submitted his complaint to the Cologne administrative court on Wednesday.
Imam Salim bin Ali Jaber and his cousin Waleed, a policeman, were killed by missiles launched from American drones on August 29th, 2012, eyewitnesses told the Süddeutsche Zeitung.
They were meeting with three men believed to have connections to terrorist group al-Qaeda.
But the imam had called on local people to stand up to al-Qaeda in a sermon at Friday prayers just days before, Ali Jaber said, and his relatives were meeting the men to respond to their questions about it.
“Were it not for the help of Germany and Ramstein [airbase], men like my brother-in-law and nephew might still be alive today,” Ali Jaber said in a statement.
“I am here to ask that the German people and Parliament be told the full extent of what is happening in their country, and that the German government stops Ramstein being used to help the US' illegal and devastating drone war.”
Ramstein: a node in the drone net
The American airbase at Ramstein, Rhineland-Palatinate, is the largest US overseas airbase and a keystone of the unmanned aircraft programme.
All the data used to control the aircraft and all the images they record are transmitted from the drones via satellite to the base's Air and Space Operations Centre, and from there by fibre-optic cable to pilots on the US mainland.
Now Ali Jaber wants the German government to prevent such data transfers through its territory, saying that his countrymen are entitled to the right to life enshrined in the German constitution.
He is being supported in the case by human rights organizations Reprieve and the European Center for Constitutional and Human Rights (ECCHR).
Kat Craig, Legal Director at Reprieve, said: “The evidence that Ramstein is a crucial peg in the US drone war is overwhelming. It’s now incumbent on the German courts to uphold the principles that are enshrined in German law that make German complicity and co-operation in killing people like Salim and Waleed unlawful."
"Faisal approached Reprieve about representing him, including in legal proceedings, to get some semblance of justice for his relatives and the communities in Yemen that are being so devastated by US drones."
Andreas Schueller, from ECCHR, addedd: “Ramstein is crucial for US drone warfare. Germany has to bring it to an end – if not it is complicit in the death of civilians."
The US government has repeatedly defended its drone war saying it takes "extraordinary care" to comply with international law.
It argues the drone strikes which target terror suspects were the course of action "least likely to results in the loss of innocent life".
This is not the first court case brought in Germany over the use of its territory to support drone strikes in the Middle East.
In 2013, federal prosecutors found that a drone attack on a German jihadist in Pakistan was not a war crime, as the man was a member of an armed group.
American forces in Germany have been regulated by the Nato Status of Forces agreement since the 1950s.
The document provides that “military forces and civilian personnel are allowed to take required measures for the satisfactory fulfillment of its defence obligations on the provided premises.”
Legal experts have previously said that a successful challenge to US military activities on German soil would have to show that a crime was committed under international law.
Meanwhile, the German government has claimed in the past that it has “no knowledge” of the use to which the US facilities at Ramstein are put.
And on a state visit in June 2013, US President Barack Obama told journalists that Germany is not used as a “launching point” for drone strikes in the Middle East when challenged about the use of the base.
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