Brazilian police arrested a woman accused of poisoning a Christmas cake with arsenic, resulting in the deaths of three family members and the hospitalization of three others during a December 23 gathering in Torres.

Authorities suspect the arrested woman, reportedly the daughter-in-law of the cake’s baker, researched arsenic online before the incident.

Toxicology tests revealed extremely high arsenic levels in the victims’ blood and the cake.

Despite a seemingly harmonious family dynamic, police cited long-standing tensions as a possible motive, CBS News has reported.

An earlier death in the family, previously ruled natural, is now under investigation for possible poisoning.

Written by B.C. Begley