Police arrested the 36-year-old man from the eastern town of Günthersdorf on Thursday after a six-month investigation that spanned two continents. He admitted to posting photos on the internet of himself sexually abusing his son, Klaus Wiechmann, public prosecutor in Halle, told The Local.

Canadian authorities found the photos, about 30 in all, on the internet and realized they were probably from Germany, Weichmann said.

“For a start, it was this soda bottle, where you could see who the maker was,” he said.

Though the soda – a raspberry lemonade from German maker Frankenbrunnen – is available throughout Germany, it is especially popular in Saxony, Wiechmann said. German Federal Criminal Police Office investigators recognized the drink and were also able to identify a schoolbook in the pictures as being from elementary schools in Germany’s former east.

Investigators showed a picture of the child to teachers in 600 elementary schools in the eastern German state of Saxony-Anhalt, Wiechmann said. One was able to identify the boy, who was 9 years old in 2003, when investigators believe the sexual abuse started. Prosecutors say the abuse continued until this year.

The boy’s father appeared before an investigating judge on Friday and remains in custody, Wiechmann said. The investigation is ongoing. Wiechmann declined to comment on whether investigators believe other children were involved, but the boy is the man’s only son.