Now, investigators have accused dos Santos of orchestrating the murder and say that at least 10 of their children were involved in the plot.
On Monday, five more of her children and a granddaughter were arrested amid reports that she had tried to kill her husband at least five times, including efforts to poison him as well as stage fake break-ins.
"The conclusion reached by the investigation was this: she planned this cowardly murder," Antônio Ricardo Lima Nunes, a homicide chief, told reporters as the singer's handcuffed relatives were led away by police.
As a federal congresswoman since 2018, dos Santos has immunity from being jailed as a suspect.
Dos Santos, who was raised in a favela, has always denied being involved in her husband's killing.
But investigators found inconsistencies between the congresswoman's story and testimony taken from her children.
One of the investigation's theories is that the couple were engaged in a battle over control of their church's finances.
Evangelical churches have considerable financial and political power within Brazil, with members often donating a 10th of their income to the institution.
The homicide chief said: "She was unhappy with the way in which pastor Anderson lived his life and handled the family finances."
"Our investigation shows that this image of altruism and decency was just a front to obtain a political and economic position," said Allan Duarte, the police chief in charge of the investigation.