A young man tried to commit suicide reportedly after killing his stepmother, stepbrother and stepsister at Khadimpara of Sylhet city early Friday.
The deceased were identified as Rubina Begum, wife of Abdal Hossain Khan Bulbul, their daughter Maha, 9, and son Tahsan, 7.
Police said Ahbab Hossain hacked his stepmother and two step siblings around 12:30am, leaving them dead on the spot.
Later, he locked his room and set it on fire.
Locals and police rescued Ahbab and later police arrested him, said officer-in-charge of Shah Poran Police Station Syed Anisur Rahman.
He said they recovered the bodies and sent those to Sylhet MAG Osmani Medical College Hospital for autopsy.
The OC said the incident took place over family feud.