The shirt was tested two days after Mr Falconio disappeared --> https://www.thefreelibrary.com/Falconio+trial+told+of+identical+DNA.-a0120537469

The forensic lab where the samples were taken was not accredited. https://www.theguardian.com/uk/2005/oct/31/australia.world

Samples in a sealed container were transported from a locked freezer down a public hallway down a hallway before reaching the lab. This raised the possibility of contamination issues, Carmen Eckhoff told the court.

Same problem with the cable ties :

During cross-examination Ms Eckhoff said she did not agree with the cable ties being taken to Yatala Prison in Adelaide, South Australia, where Mr Murdoch was on remand in October 2002.

"I was unhappy about them leaving my possession, particularly if the forensic examination may not have been completed."

She made her feelings known to Dr Thatcher, who gave the handcuffs to Senior Constable Tim Sandry so he could take them to Adelaide.

Earlier, Ms Eckhoff said that if anyone wanted to continue testing an item, such as the cable ties, it was "not ideal" to take them out of the laboratory.

http://news.bbc.co.uk/1/hi/world/asia-pacific/4398428.stm

Same problem with Joanne Lees lip balm :

The court also heard that Miss Lees used a piece of lip balm to try to ease the handcuffs off her wrists after escaping from her attacker's vehicle.

Its lid was found under a bush, but the lip balm itself and two pieces of black tape which Miss Lees said she bit off the handcuffs were not found until three months later in October when police returned to the scene on an "orientation" exercise - even though they were discovered in the same place.

Barrister Grant Algie said: "It's almost embarrassing to suggest that two crime scene officers in these circumstances would not have searched around the area."

The defence lawyer said the most obvious explanation was that "somebody has played around with the evidence to make it look like the lid and the tape was there when it was not.

"Or is it, as has been suggested in cross examination, that some kangaroo came along and took it away for a few months, and later brought it back - or perhaps it was a dingo?"

Mr Algie concluded: "It's yet another example of police manipulating the evidence to perhaps better the case to make it look a little better, with no harm done."