The husband of an Alabama mom-turned-online porn star was arrested for her murder Thursday — a month after her half-naked body was found in the street outside their home.

Cops say they finally cuffed William “Jeff” West, 44, for killing his wife, Kathleen West, after securing a key piece of forensic evidence the day before — but wouldn’t say how or why he did it.

“We know what happened that night and we do have evidence to support that,” Calera Police Chief Sean Lemley said at a press conference. “But providing that evidence may hinder prosecution.”

Lemley did reveal that the cause of death was blunt-force trauma to the head.

He said the husband was a suspect from the very beginning, but it took a while to work out exactly what had happened because Kathleen’s body had been found in the street — not at home, where domestic violence usually takes place — and because she wasn’t fully clothed.

He added that cops had spoken to Jeff twice before his arrest and “he didn’t seem to be very upset.”

In real life, Kathleen was a self-described full-time mom and wife. But online, she posted racy images to a private Instagram account with nearly 52,000 followers — and promoted a $15.99-per-month subscription deal for “naughty fun.”

Asked whether her double life played a role in the killing, Lemley responded carefully: “I think her online profession, her activities, certainly warranted a lot of attention.”

The couple had been recorded looking happy on security footage at a liquor store the night before Kathleen’s body was found, and Lenley said cops didn’t know exactly how things went south between then and her death.

“Unfortunately, domestics turn bad pretty quickly,” he said.