Nick Gordon (L) and Bobbi Kristina Brown attend the opening night of "The Houstons: On Our Own" in New York
Nick Gordon (L) and Bobbi Kristina Brown attend the opening night of "The Houstons: On Our Own" in New York October 22, 2012. Reuters/Andrew Kelly

The mystery surrounding Bobbi Kristina Brown's death refuses to die down anytime soon. New court documents have revealed that Brown's longtime boyfriend Nick Gordon allegedly injected her with a lethal substance, which caused her death later.

The daughter of late singer Whitney Houston and Bobby Brown allegedly died due to "injection of a toxic mixture" by Gordon, which left her unconscious in her bathtub, according to court documents filed by Brown's court-appointed conservator Bedelia Hargrove. The documents were obtained Thursday by WSB-TV in Atlanta.

"Ms. Brown died due to a violent altercation with Defendant (Gordon) after which he placed her in a bathtub, unconscious, after he injected her with a toxic mixture," read the documents obtained by the website.

Gordon earlier requested court to stop the lawsuit filed by Brown's camp that claimed he had a hand in the "wrongful death" of the 22-year-old. The new filing by camp Brown on Thursday came in Gordon's earlier response and argues that his request to halt the legal proceedings in the civil lawsuit should be denied.

However, it is for the first time that a mention of injection has been made. Earlier Brown's estate had alleged that Gordon accepted US $40,000 (AU$ 50,000) from a magazine so that they could photograph him at his girlfriend's grave.

According to People magazine, Gordon's lawyers have called the latest accusations as "meritless and slanderous."

The lawsuit filed against Gordon in August also claims that she died "after a particularly violent altercation with the Defendant (Gordon) which left her battered and bruised, with a tooth knocked out." Gordon has also denied this accusation.

Brown passed away on July 26 in a hospice after spending nearly six months in coma. She was found unresponsive and face down in a bath tub in her Roswell, Georgia home she shared with Gordon.

Contact the writer at feedback@ibtimes.com.au, or let us know what you think below.