A German teenager accused of killing a child and a 22-year-old acquaintance, then posting pictures of the crimes online, is going on trial.

A 19-year-old man arrested over the death of a neighbour's son has admitted killing the child as well as a 22-year-old acquaintance, prosecutors in western Germany said.

A man has been arrested during a German police search for a suspect over the killing of a nine-year-old boy.

A photo showing the suspect - named by police as Marcel Hesse - bragging about the killing was circulating on the so-called darknet.