GENEVA — German authorities announced the arrest on Wednesday of a former high-ranking Syrian intelligence officer and two subordinates suspected of crimes against humanity by torturing thousands of victims in detention centers run by President Bashar al-Assad’s security services.

The arrests were a result of a joint investigation by German and French prosecutors, the office of Germany’s federal prosecutor said in a statement on Wednesday. The German police had arrested two suspects, identified as Anwar R., 56, and Eyad A., 42, and placed them in pretrial detention, the statement said. Officials decline as policy to give the full names of suspects pending the outcome of legal proceedings against them.

They said the French police, “as part of a joint investigation team,” had detained a third suspect who was linked to Anwar, but gave no other details.

The man identified as Anwar R. “is the most serious regime perpetrator detained so far by some distance,” said William Wiley, a former war crimes prosecutor who leads the Center for International Justice and Accountability, a group collecting evidence of Syrian atrocities. “It’s a big day for everyone working on these issues since 2011, really big.”