Sarawak police last night detained a police inspector who was believed to have shot dead his girlfriend.

He was detained six hours after the incident took place.

Sarawak Police Commissioner Datuk Mazlan Mansor said the man in his 30s was arrested at about 9.35pm, Sunday near the e-Mart Matang supermarket.

He said police are now focusing on the motive behind the incident.

"The investigation is now focused on the personal problems between the suspect and the victim," he told Astro AWANI when contacted.

Mazlan did not state if the gun used in the murder has been retrieved from the suspect.

The suspect is an inspector based in Belaga.

In the incident at about 3.15pm, a woman was found dead in her family home at Kampung Kakai, Serian, believed to have been shot dead by her boyfriend.

The victim, Siti Nadirah Abdullah, 33, was believed to have secretly married the suspect.