Raslan, who defected from the Syrian regime in 2012 and fled the country, had denied all the charges against him.
The landmark ruling comes as the Assad regime -- accused of killing hundreds of thousands of civilians with conventional and chemical weapons -- has been repairing diplomatic ties with former regional foes, such as the United Arab Emirates and Saudi Arabia.
The United States and the European Union have criticized its Arab allies for bringing Assad into the regional fold, but have said they can do little to stop the rapprochement.
The court in the German town of Koblenz drew on nearly 100 testimonies, according to lawyers representing the plaintiffs. Several survivors of torture at Branch 251 took the stand and came face to face with their alleged persecutor.
They offered detailed accounts of physical and psychological abuse, as well as severely overcrowded cells where they were deprived of food, water, and medical treatment.
One unnamed female witness described being examined naked, as well as being beaten at the detention center. She detailed her encounter with Raslan after having been taken to him with her clothes torn from the assault, saying he ordered her blindfold removed, and offered her coffee.
The next day, according to a summary of her interactions with Raslan by the European Center for Constitutional and Human Rights, she was transferred to another district and released.
Co-plaintiff Wassim Mukdad, a Syrian musician living in Berlin, said he was hit on the soles and heels of his feet and his knees during interrogations. "They knew exactly how to inflict maximum pain," he told the court.
In their closing statements, the plaintiffs delivered emotional speeches, praising the court and berating Raslan for denying the charges against him. More than 100,000 people are believed to have been abducted, detained, or gone missing in Syria, the United Nations has said, and one co-plaintiff criticized the judicial process for excluding enforced disappearances from the charges.
The co-plaintiff, Hussein Ghrer, recalled that his captors at the detention center said he would "disappear behind the sun." He told the court that to his loved ones he was like Schrödinger's cat, appearing both alive and dead at the same time. He said he was "banished from life without actually dying."
"Regardless of how long [Raslan] will be imprisoned, he will have a clock near him, he will see the sun and know when it rises and when it sets," Ihrer told the court. "He will have medical care when needed, and he will receive visits from relatives who will know how he is doing, just as he will know how they are doing."
Raslan's trial was seen as the culmination of nearly a decade of evidence collected by activists and lawyers seeking to hold the Assad regime accountable for alleged war crimes and crimes against humanity.
In the early years of Syria's uprising-turned-war, which began in 2011, volunteers known as "document hunters" smuggled out hundreds of thousands of documents from abandoned regime facilities. Many said they braved an onslaught of bullets and rockets to smuggle out papers that served as evidence in investigations against the regime.
In 2013, a defector codenamed Caesar smuggled tens of thousands of photographs showing prisoners allegedly tortured
to death in Assad's jails. The images were also part of the evidence in the landmark trial.
Lawyers and activists vow to continue to pursue the prosecution of former and current regime officials implicated in crimes. In Germany, Raslan and Gharib were arrested under the principle of universal jurisdiction, which gives a state jurisdiction over crimes against international law even if these did not occur inside that state.
The Syrian regime cannot be tried at the International Criminal Court because it is not a party to it. Syria could be investigated by the ICC if the United Nations Security Council refers it, but Russia and China have blocked a previous attempt to do so by the UNSC.
In July 2021, a German prosecutor indicted a Syrian regime doctor, Alaa Mousa, who is accused of burning the genitals of at least one prisoner. His trial begins in Frankfurt this month.
"We all agree that this can only be the first step," Patrick Kroker, a lawyer with the European Center for Constitutional and Human Rights representing the joint plaintiffs, said in a Monday news conference. "There are international arrest warrants still outstanding against even higher-ranking persons and we hope and we demand that these will be pursued.
"There will be no haven in the world for these people."