German police have arrested a man who was sexually abusing his "companion's" four-year-old daughter, after coming across a video of the abuse the suspect had uploaded on the dark web, a section of the internet where people contact each other anonymously without the fear of being monitored.

Though authorities had first spotted the footage in July, they were unable to identify the offender. However, the man was arrested a few hours after the authorities took the drastic step of publishing several grabs of the girl from the video, asking the public for help, prosecutors said Tuesday.

The authorities feared the girl could still be accessible to her attacker and therefore in the last ditch effort, Generalstaatsanwaltschaft Frankfurt am Main (Frankfurt Attorney General) and Federal Criminal Police Office or Bundeskriminalamt (BKA) decided to go public  with images of the young victim Monday in a bid to identify her. 

They said, "Since there are no further investigative possibilities, the District Court of Giessen ordered a public inquiry with pictures of the victim," the Sun reported. 

"It is very rare that we go public with pictures of the victims. This really only happens when all further investigations are exhausted and we see no other way to identify the perpetrator," said chief prosecutor Georg Ungefuk from the Central Office for Combating Cyber Crime

The ploy worked and the man was turned in by the mother and grandparents of the little girl before midnight Monday, Bild reported.

German’s Federal Crime Office released a statement revealing that the suspect is a 24-year-old German citizen who was detained from his home in the northern county of Wesermarsch in Lower Saxony on Monday, Kansas City Star reported. 

The offender was identified as the girl's mother’s "companion."  

Police said they found evidence in the offender’s apartment which directly linked him to the crime. Authorities think the perpetrator had been abusing the girl from Oct. 2016 till July 2017, filming it and uploading the recordings on child pornographic platforms on the dark web.

“The girl was examined by a police psychologist and is now again in parental care. It is not decided whether she will be medically examined tomorrow (Oct.11)," Ungefuk said,

A BKA spokesperson told Bild, “We are grateful that our public prosecution has led to success so quickly. Of course, further investigations are on course.” 

The dark web is a section of the internet where people contact each other anonymously without the fear of being monitored. The site is easily used by criminals to sell illegal drugs, chemicals, weapons, child abuse images and even offer assassination services.