In each of the decisions since September, the acquittals followed failed bids in state appeal courts.

But lawyers say despite the cluster, those decisions are still rare given the hurdles appeals have to overcome to even get before a full bench of the country's top judges.

Five convictions against Cardinal Pell for child sexual abuse were unanimously quashed on Tuesday after the seven judges found there was insufficient evidence for a jury to reach a guilty verdict beyond reasonable doubt.

In February a full bench of five judges acquitted former London metropolitan police officer Eamonn Coughlan and quashed convictions for arson and attempted fraud.

The Brisbane man was jailed for three-and-a-half years last July after being found guilty of blowing up his Queensland home in an attempt to make a fraudulent insurance claim.

Mr Coughlan lost a bid for freedom in the Queensland Court of Appeal.

He maintained his innocence and blamed the arson prosecution on local police corruption.

The court is yet to publish its reasons in Mr Coughlan's case, but ordered his acquittal and release from jail at the end of his one-day appeal hearing.

No expert had examined the remains of the home, the possibility it was destroyed by a gas leak weren't adequately explored and there were no attempts to exclude innocent explanations for petrol residue found on his clothes, his lawyer Stephen Keim SC argued.

In a separate Queensland case in September last year the High Court overturned a jury's verdict over the 2012 death of Queensland grandmother Liselotte Watson.

Steven Fennell was convicted of murder and jailed over the "cruel and callous" killing in 2016, but the High Court ordered his acquittal after determining the murder weapon evidence was "glaringly improbable".

The weapon, a hammer, was found a short distance from items that belonged to Mrs Watson.

A couple identified it as being a hammer they loaned to Mr Fennell years before the murder.

"Their evidence should have been given so little weight that, at best, it was barely admissible," the High Court said.

He too had argued to the Queensland Court of Appeal that the jury's verdict was unreasonable, but turned to the High Court after that appeal failed.

Australian Associated Press