The investigation into the circumstances that led to Bobbi Kristina's death yesterday Sunday July 26 has just been amped up ... It is now officially a homicide investigation. TMZ reports below...

Law enforcement sources tell us, both the D.A. and the cops are treating the mystery as foul play, and Bobbi Kristina's boyfriend, Nick Gordon, continues to be a person of interest. Although months have separated the incident in which Bobbi Kristina was found submerged in her bathtub from her death Sunday, law enforcement is confident there will be no problem finding a direct link between the 2, and they have felt from the beginning there was foul play.

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