The twin brothers at the centre of Friday's tragic fatal shooting south of Adelaide had experimented with the same drug as Cy Walsh used before he stabbed his father to death, Seven News can reveal.
Jake and Lucas Cawte document their South American spiritual journey.
The 24-year-old's weren't just twins – they were best mates.
But something set Lucas off Friday morning when he allegedly shot Jake in the head, killing him at the family home in Willunga before handing himself in.
The men's distraught mother told 7 News that while in South America, they had experimented with the powerful hallucinogenic drug "ayahuasca".
It's the same drug Cy Walsh had taken in the years before killing his father.
After hearing about Phil Walsh's death in 2015, the Cawte family became worried about Lucas and Jake's state of mind.
They had returned from their trip different people.
"They have changed their outlook on life completely," forensic toxicologist Andrew Leibie said.
"They feel like they're a different person based on the things they've seen and perceived while they're taking this drug."
Lucas has also been battling mental illness and had been in and out of the Margaret Tobin Centre at Flinders.
He is being held at the centre again following his arrest.
His mother says she is desperate to visit him and is vowing to "wrap her arms around him and stand by him… no matter what he's done."
The men's mother hopes the tragedy will serve as a warning about the dangers of hallucinogenic substances.
It's understood the men's father keeps guns at the property but it's unclear if one of them was used to kill Jake.