The arrestee was identified as Samiul Islam Sagar, 22, son of Jan Mohammad of Chawkshamra village of the upazila.
Manda Police Station’s Officer-in-Charge Mozaffar Hossain said Sagar had an affair with the rape victim. On Monday night, the girl and her mother Nasima Akter Sathi, 40, were sleeping in their house when Sagar came in.
Sathi’s husband Emdadul Haque works as a night guard at a farm in Natore.
Sagar went to victim’s house with an intention to kill her as their relationship was going through a bad patch.
Sathi woke up hearing an argument between her daughter and Sagar in the middle of the night. The youth stabbed her with a knife and slit her throat. He then threatened to kill the girl and raped her.
Police arrested the young man soon after the incident. OC Mozaffar said that Sagar had confessed to his crimes during primary interrogation.
The body was sent to the Sadar Hospital for autopsy and the rape victim was sent for medical tests, he said.
A case has been filed over the rape and murder.