As Bobbi Kristina Brown's family and friends mourn her passing Sunday night, the cause of her death – and the reason she was found unresponsive in her bathtub on Jan. 31 – remains a mystery.
According the Fulton County Medical Examiner, there will be an investigation into her "non-natural death."
The medical examiner's office, in a statement obtained by PEOPLE, states that: "The death of Bobbi Kristina Brown has been reported to the Fulton County Medical Examiner's Office in accordance with state death investigation laws requiring investigation of known or suspected non-natural deaths. Because the events at her home leading to her death occurred in Fulton County (Roswell), her death has been reported to the Fulton County Medical Examiner for determination of the cause, manner, and circumstances of death. Despite the long interval between her being found unresponsive and her death, an autopsy will still be necessary to further evaluate possible causes of death or contributing factors."
The statement added that the months between the January incident and the 22-year-old's death will "complicate reconstruction of the events surrounding her initial unresponsiveness. Interpretation of autopsy findings and other information will also be challenging. However, an autopsy could be helpful to address questions which may arise about the cause of her unresponsiveness and eventual death."
On Monday afternoon, the office updated their statement, saying, "The initial portion of the autopsy has been completed. The autopsy does not show an obvious underlying cause of death and no significant injuries were noted. No previously unknown medical conditions that could have contributed to death were identified. Additional laboratory testing will be performed. Subpoenas have been issued to obtain needed documentary information."
"We do not plan to complete the death certificate or determine a cause and manner of death until all test results are completed and all investigative, medical, and other documentary records are received and thoroughly reviewed," the statement continues. "We anticipate that these processes will take several weeks."
Additionally, according to the statement, the Roswell Police Department "continues its investigation into the circumstances preceding and surrounding the time of the original incident leading to her death."
The daughter of the late Whitney Houston and Bobby Brown had struggled following her mother's 2012 death. She developed substance abuse issues, and used heroin, cocaine, and Xanax in the months leading up to the January incident, according to sources.
On Sunday, a family member said that in her death, her loved ones were taking solace in the fact that she was finally at peace.
Said the family member: Bobby is "very emotional, but at the same time, he knows that Krissy is in a better place now. He is taking comfort in the fact that she's with her mother, and that there will be no more sadness or pain."
Reporting by ELISSA ROSEN