Authorities in the German town of Karlsruhe on Thursday detained a 31-year-old woman who had recently returned from working on behalf of the so-called "Islamic State" (IS) group in Syria.

Authorities were only allowed to arrest the woman — identified as Sabine S. in accordance with the German press code — at the second time of asking.

An initial warrant for her arrest was denied earlier this year after a judge had ruled that simply living in the IS-controlled territory was not enough to justify her arrest.

In a subsequent investigation, prosecutors found that Sabine S. had traveled from Germany to Syria in late 2013, where she went on to marry and have two children with an IS soldier. The man was killed in December 2013, although she is believed to have married again afterwards.

The woman was tasked with promoting life in the jihadi caliphate on an online blog monitored by the jihadi group. It was there that she also expressed her willingness to attack enemy combatants by carrying out suicide attack.

The evidence was enough to warrant her arrest.

As the jihadi group lost its grip on territories, Sabine S. was detained by Kurdish forces in September 2017. After being released she was free to travel back to Germany and reportedly arrived back in Karlsruhe in April 2018.

Sabine S. is the second German woman to be prosecuted for actively working on behalf of IS in Syria. Last month, police arrested 27-year-old Jennifer W., after it emerged that not only had she traveled out to Syria to live with IS militants; she was also part of an IS patrol group, effectively working as a policewoman inside the jihadi caliphate.

Read more: Children of 'Islamic State' struggle to integrate in Germany

In July, Jennifer W. became the female citizen prosecuted by German authorities for overseas involvement with the "Islamic State" group.

Murder charges filed against German IS militant Nils D.

Also on Thursday, the Federal Public Prosecutor's Office brought fresh charges against former IS fighter Nils D., who has already served two years of a four-and-a-half-year prison sentence in Düsseldorf.

New evidence suggests the 27-year-old murdered three people while fighting for IS in Syria, unprovoked and in cold blood.

Nils D., traveled out to Syria in late 2013 and joined IS in March 2014. He was part of a special unit tasked with arresting deserters and maintaining their prison cells. It was there that he is suspected of having brutally tortured and killed three people.

He returned to Germany by the end of 2014 and agreed to cooperate with German authorities after he was arrested.

Nevertheless, in 2016, he was still sentenced to four-and-a-half years in prison for joining a foreign terrorist group. The new charges, which violate the International Criminal Code, could see his sentence extended.

Editor's note: Deutsche Welle follows the German press code, which stresses the importance of protecting the privacy of suspected criminals or victims and obliges us to refrain from revealing full names in such cases.

Former IS fighter Nils D. covers his face as he appears before a court in Düsseldorf.

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dm/bw (dpa, AFP)