"Foul play is begin investigated," a family source tells PEOPLE. "Including drug use and possibly cover up to remove evidence from the crime scene."
At the center of that investigation is Bobbi Kristina's boyfriend Nick Gordon, a source with knowledge of the case told CNN. Another source close to the family told the news network that the 21-year-old daughter of Whitney Houston had "injuries that still need to be explained."
In addition, law enforcement insiders told TMZ that police are looking into a possible altercation between Bobbi Kristina and Gordon more than an hour before she was found unresponsive. Multiple sources told the site that there is a history of violence between the two.
According to TMZ, Max Lomas, the friend who discovered Brown's body with Gordon, claims that he saw Gordon cleaning blood stains.
Roswell Police Chief Rusty Grant told PEOPLE that the police are "going to follow the evidence and see where it leads us."
Family members gathered at Bobbi Kristina's bedside throughout the past week to offer their support.
In an emotional Facebook post on Thursday, her cousin Jerod Brown asked fans to pray for a miracle.
"Though it seems the odds are against her, though doctors don't see any hope for change, though we might want to play detective and find out how she got there, though it looks impossible for her to stand again STILL PRAY FOR BK," he wrote.
Lawyers for Bobby Brown and Max Lomas did not immediately respond for comment.
For more on Bobbi Kristina, pick up the new issue of PEOPLE, on newsstands now
Reporting by LIZ MCNEIL
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