Eight years after her husband's death after taking cyanide-laced food, a woman and two others were arrested on Saturday, and investigations into the death of five others of the family were on, police said.
Confirming the arrests, Kozhikode rural superintendent of police K G Simon told reporters the arrests were in connection with the death of Roy Thomas in 2011, and the prime accused in the case was his wife Jolly with whom he was not having a good relationship.
The two other accused - M S Mathew (44), a close friend of Jolly, and Prajikumar (48) - had allegedly supplied the cyanide to Mathew who handed it over to Jolly.
For the past two months, a special investigation team, based on a complaint from Roy's US-based brother, has been probing into the case of six suspicious deaths that had occurred between 2002 and 2016.
While Annamma Thomas had died in 2002, her husband Tom Thomas died six years later in 2008.
Later, their son Roy Thomas died in 2011.
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Annamma's brother Mathew died in 2014 and two relatives - Sili and her one-year-old daughter in 2016.
As police found that the deaths were suspicious, the remains of the six were exhumed on Friday and forensic reports were awaited, Simon said.
In all the cases, traces of cyanide had been found and it was a case of slow poisoning, police said.
"We found that the Roy's death had occurred due to cyanide, while the wife had claimed that he had died of cardiac arrest," he said.
"We felt that the case had to be re-investigated," he said, adding six people had died in similar circumstances over a period of about 14 years.
"But those deaths were not investigated. We found similarity, a pattern and the presence of one person in all the cases - Jolly," he said.
After the death of her husband, Jolly had got married to Sili's husband.
Police said Jolly, who was a commerce graduate, had claimed she was an engineering graduate and was working as a lecturer at the National Institute of Technology (NIT).
She used to travel everyday in her car to the institution.
Police said Annamma Thomas, who was the power centre of the family, was killed to claim her money, while it is suspected that Tom Thomas, a retired government employee, was done to death to get more share of the property.
Roy was killed as the accused was not getting along well with her husband.
Annamma's brother Mathew had insisted on postmortem of Roy, due to which he was killed, police said adding Sili and her one-year-old daughter were also killed in similar circumstances.
DGP Loknath Behra congratulated the probe team for cracking the case.