A Compton man who killed his wife of 30 years by slitting her throat the day after her 58th birthday pleaded guilty Monday to second-degree murder.

Henry Cunningham, 66, is scheduled to be sentenced Sept. 4 for killing Melanie Ann Cunningham. Under the terms of his plea deal, he faces 15 years to life in prison.

Melanie Cunningham was asleep in a bedroom with her 1-year-old granddaughter on Dec. 17 when Cunningham grabbed a kitchen knife and slit her throat, according to Deputy District Attorney Van Ha.

Authorities said the granddaughter was not hurt. The motive for the killing was unclear.

The couple lived in the 15600 block of South Frailey Avenue near where Alondra Boulevard crosses the 710 Freeway, about a mile above Long Beach’s northern city limits.

Los Angeles County sheriff’s deputies sent to the couple’s home found the woman dead at the scene and arrested her husband.

The woman had turned 58 a day earlier, and the couple had celebrated her birthday that night, according to a family member.