The pair were discovered at their flat in Hanover, capital of Lower Saxony, on Tuesday evening, after a relative saw the bloodied body of one of the victims through a window and rang the emergency services.
Firefighters were called in to capture the dog who was still inside the residence, Hanover police said in a statement.
Fire personnel broke down the door and caught the dog by using a sling.
“Initial examinations by a coroner suggest the 52-year-old woman and her 27-year-old son were killed by the dog,” it read.
Police investigations into the incident are continuing, the statement added.
A law change implemented several years ago means that all dog owners in Lower Saxony have to obtain a Hundeführerschein (dog holding licence) when they buy a canine.
To obtain the licence, owners have to pass a theoretical test before they buy the dog and a practical test within a year of purchasing the animal. The licence was instructed in order to bring down the number of deaths and injuries caused by attack dogs.