The Faustin House Blood Trail refers to two parallel trails of what is presumably blood found at the back of Mikhail Faustin's patio, beginning at the patio doors and ending just before the patio step at the rear of his property.
Players have claimed that the trail is only visible after the mission Crime and Punishment, wherein Mikhail shoots his henchman Andrei in the head and kills him. Players theorized that the trail suggested Mikhail, Dimitri or another of Mikhail's henchmen dragged the body of Andrei through the patio area and most likely dumped it over the cliffs into the sea surrounding the rear of Faustin's property.
They have also claimed that the body of Andrei, along with a considerable amount of money and weapons could be discovered at night, on the nearby beach and in the bushes surrounding the house.
However, this entire theory has been proven to be false, as the trail is visible from the very start of the game, leaving the source of the blood unknown and the mystery open. And there is no evidence to prove that Andrei's body can be found there.