A mother and her baby girl have been found dead in Sydney's inner west.

Police are investigating the deaths of the Sydney mother and daughter, in what’s  believed to be a murder-suicide.

In this photo, the Nguyen family look just like any other.

To the outside world, Sydney father Quyet, his 29-year-old wife, Phoung, and their 18-month-old daughter, Sienna, were just another average Sydney family.

But yesterday, a tragic suspected murder-suicide left the image of a happy family a mere memory for traumatised Quyet and their relatives.

Phuong and Sienna were found dead in the family home in Fitzroy Street, Campsie – a suburb in Sydney’s south-west – by a relative early yesterday afternoon.

Phuong was pronounced dead at the scene and paramedics desperately, but unsuccessfully, tried to revive the baby girl.

A distraught Quyet arrived home to the news in the afternoon, collapsing in front of the police tape that cordoned off his home.

Today, it is a crime scene.

Relatives and friends are dumbfounded by the loss of Phoung and Sienna – who happily celebrated her first birthday in the Campsie backyard earlier this year.

They surrounded the house with flowers, incense and prayer books to support the grieving husband and father.

“I don’t think he’s understood what happened yet, I think he’s still in denial,” an associate identified as Dang told The Daily Telegraph.

“He’s very upset.”

“We just don’t understand why this has happened.”

And that’s exactly what detectives – who are investigating whether post-natal depression or mental illness played a role in the tragedy – are trying to figure out.

A friend said she had “no idea” whether Phoung was struggling to care for her young daughter.

“What I can tell now is it is all bad news and it is very sad for everyone,” she told Fairfax Media.

Our thoughts are with the Nguyen’s loved ones at this terrible time.

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