Audrina Patridge's 15-year-old niece Sadie died from drug overdose - and police are investigating possible criminal charges

Audrina Patridge's 15-year-old niece Sadie died of a drug overdose nine months ago it has been revealed.

Now police are currently looking for who may have supplied the narcotics which killed the teenager according to law enforcement sources in a TMZ  report on Monday.

 Though Sadie's death has been officially ruled a narcotic overdose, the manner of death has still yet to be determined pending the possibility of criminal charges.

Insiders for the publication say that law enforcement would like to figure out how Sadie was able to obtain the drugs. 

TMZ's source claimed to the publication that the teenager was able to buy Percocet through Snapchat and it was laced with fentanyl.

If indeed that is the case then police will investigate who sold it to Sadie and charges are likely to follow. 

Back in February Patridge, 38, announced the death of her 'beautiful' niece Sadie on Tuesday - just nine days after the teenager turned 15. 

The former The Hills star shared a heartbreaking tribute to her beloved niece and a montage of photos taken with Sadie over the years.

She wrote: 'My heart hurts to even write this. My beautiful niece is now in heaven. 

'I know its not goodbye forever, but it is the hardest to say goodbye for now. We will miss you and cherish every single moment we had with you. Rest in peace Say Say!! We love you forever & ever! '

The photos included snaps of Sadie at Audrina's wedding to Corey Bohan in 2016 and a video with Sadie and her mother and Audrina's sister Casey. 

Her Hills co-stars Brody Jenner and Kristen Cavallari posted messages for Patridge and her family on social media following the shock news, along with a string of other celebrities including Rachel Bilson and Ashley Greene. 

Casey, who appeared with Audrina on The Hills and The Hills: New Beginnings, confirmed Sadie's death on Instagram and shared a heartfelt tribute.

She wrote: ‘Sadie Raine Loza has left this Earth for the heavens.

‘Writing this was the hardest thing I ever have had to do, not knowing the right words I’ll leave you with this.

'Sadie liked to remind me that the first law of thermodynamics aka (Law of Conservation of Energy) works in all spheres of life…..”Energy cannot be created or destroyed, it can only be changed from one form to another”. ‘ 

‘Transformation is a better word than death. Her story will save countless lives, her memory will never be forgotten. 

'Rest In Peace you brilliant starseed. You’re with your creator. We will miss you dearly. I love you.’

Nine days before Sadie's death, Casey marked her 15th birthday with a video of the teenager blowing out candles on her birthday cake.

She wrote: 'Cant believe you're 15. it feels like the years flew by and we still have so many more adventures to go on!

'Aliens in sedona, portals, learning to drive in the desert hahah i love you so much my little clone. you're so beautiful, kind, smart and funny!! 

'I'm so proud to be your mom and i cannot wait to see the insane ancient civilization architecture you’re going to construct someday. i love you so so much my Sadie Raine. 

Casey is also mom to a son with her husband Kyle Loza.