The law enforcement agency also recovered looted gold ornaments and money from their possessions.
The arrestees are Rekha Akhtar and her Husband Ershad.
Shahjahanpur Police Station under the Dhaka Metropolitan Police (DMP) conducted a raid at Chikon Matiya Maddhyapara of Kashipur under Ranisankail Police Station in Thakurgaon at around 5am and arrested Rekha.
Police arrested her husband Ershad from North Basabo in the capital, DMP Deputy Commissioner (Media) Walid Hosain told reporters at the DMP media centre on Thursday afternoon.
He said Rekha has been working as a domestic help at the victim’s house for the last one year.
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Mehbuba Zaman, the house owner, went to Barishal on January 17 leaving her 75-year-old mother Bilkis, sister Dilruba Zaman and Rekha at her Malibagh residence.
Rekha assaulted Bilkis with an iron rod when Dilruba went out of the house the next day. The domestic help fled after looting gold ornaments and cash worth around Tk 21 lakh.
A case was filed at Shahjahanpur police station over the incident.