Police discover critical evidence on daughter-in-law's phone following arrest over Christmas cake that killed three

The daughter-in-law accused of killing three of her relatives by poisoning a Christmas cake has been caught with startling evidence on her phone.

Three women are thought to have been murdered as they celebrated the holidays together and ate a homemade Christmas cake.

Their names are Tatiana Denize Silva dos Anjos, 43, her elder sister Maida Berenice Flores da Silva, 58, and Neuza Denize Silva dos Anjos, 65.

The traditional 'Bolo de Natal' Christmas cake had been prepared by 61-year-old Zeli Terezinha Silva dos Anjos - sister to Maida and Neuza, and aunt to Tatiana - on 23 December.

Zeli herself ate two slices and was hospitalised along with two other family members.

According to the Mail, blood tests carried out on those who ate the cake found arsenic in some of the victims, though the investigation is still determining whether those affected were poisoned. However, it appears that this could have been an alleged premeditated incident.

The cake left three dead and three more in hospital (Divulgação/Polícia Civil)

The Mail reports that the daughter-in-law of Zeli has since been arrested on suspicion of murder and attempted murder, with her mobile being seized and searched by Brazilian officials.

The woman is married to Zeli's son, and the Mail reports that Torres police chief, Marcus Vinicius Veloso, told them she had been arrested at her home on Sunday (5 January), saying: "The woman was arrested for triple homicide and a triple attempted homicide.

"She was taken initially to a police station at Canoas, then to Torres police station and is now in the women’s jail in the city, at this moment we cannot say anything else."

But now, more has come to light.

After an initial analysis of her phone, the woman allegedly searched for 'arsenic' and similar terms on Google shopping.

While the incident occurred in December, the searches allegedly happened in November and then days before the cake was made.

Authorities also confirmed that the source of the arsenic poisoning was the flour used to create the cake. This flour was contaminated with arsenic at ‘extremely high concentrations’ which would be lethal.

Zeli's sisters died after eating the cake (Facebook)

Forensic experts then suggested that the arsenic was intentionally added.

Veloso claimed during a press conference: "We suspect the individual arrested entered Zeli’s house and then contaminated the flour."

As for the motive, it was suggested that the woman and Zeli had a tumultuous relationship.

Veloso said: "We knew there had been minor disagreements between the suspect and elements of the family for several years. On the face of it all those at the party were close and harmonious but when we extended our investigations we found motives that were probably behind this poisoning."

Because of this tragedy, Zeli's late husband's body was exhumed as he died of food poisoning earlier in the year.

The daughter-in-law is set to appear in court for a custody hearing on Monday, 13 January.