Police attended the home of a woman at the centre of a murder and rape inquiry the day before she died.
Officers responded to a "concern for welfare" call 24 hours before Charrissa Brown was rushed to hospital on Wednesday, where she died.
They had visited her flat in Gorse Bank, Bury.
READ MORE: 'RIP my beautiful daughter': Tributes paid to woman, 36, at centre of murder and rape investigation
Now a police watchdog is investigating after GMP voluntarily referred itself to the Independent Office for Police Conduct due to the previous police contact.
In a statement the IOPC said: “We have received a referral from Greater Manchester Police regarding the conduct of officers who responded to a report of concern for the welfare of a woman who has since sadly died.
“We are assessing the available information to determine if any further action is required from us."
A post-mortem was inconclusive.
Police launched an investigation and arrested three men - aged 32, 52, and 61 - on suspicion of murder and rape.
In an update Greater Manchester Police said: "A post-mortem was inconclusive, three people are still in custody, and further investigations ongoing."
The men were arrested at properties on Gorse Bank and Rutland Drive, Bury.
The Manchester Evening News understands there were signs of possible drugs misuse inside the Gorse Bank property, which is a line of inquiry.
Touching tributes to Charrissa have now been paid as the probe continues.
Charrissa's mum Sue Brown said: 'RIP my beautiful daughter'.
She said that the tributes flooding in for her on social media show how 'special and loved she is'.
Friend Leigh Kelly wrote: "Rip Charrissa Brown absolutely heartbroken.
"Loads of memories with you.. one of the funniest girls I know.. one day we will have that catch up until then may u rest in peace and be given the best bed in heaven my girl xxx."
Sue is asking Charrissa's loved ones to leave flowers and tributes on Gorse Bank.
Investigations were continuing at the scene this morning.
Crime scene investigators have been working inside a first-floor flat.
Police also remain at the scene on Rutland Drive this morning.
A statement yesterday issued by Detective Superintendent Kate Atton, from GMP's Bury CID, said: "I have no doubt that the community are shocked and are worried to hear the news about this incident but I would like to reassure them that we have a dedicated team of detectives investigating and following up various lines of enquiry to establish the circumstances around this lady's death."
Anyone with information can report it online or by using our LiveChat service at www.gmp.police.uk. Alternatively, contact Crimestoppers anonymously on 0800 555 111
