Factual error: The movie is set in the late 90s but in the parking lot scenes, the pair are surrounded by cars as new as 2012.
Factual error: The search that cracks the case is nonsense from a simple logical standpoint. There are three people, whose deaths have never been related together, but that all died because of tetryzoline poisoning. Entering all three of those names in google would not produce relevant results or even narrow the spectrum, because it's three unrelated deaths. (01:08:40)
Factual error: The delivery van bringing gear for the walk has a 718 area code on it. That area code did not exist until 1984.
Factual error: Throughout the film, the helmet plates worn by the London Policemen are the 1930's pattern with the George V cypher in the centre. In 1912/13 they would have repeated the officer's collar number in the centre. The helmets themselves are also British military pattern blue cloth helmets with Police fittings added, rather than the correct Police pattern ones.