Newly filed TRO petition details dangerous past of Kauai murder suspect

HONOLULU (HawaiiNewsNow) – Court records are providing new insight into the criminal history of Kauai murder suspect William ‘Billy’ Sinclair.

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In a newly obtained TRO petition filed Tuesday, a woman says she and her partner faced “difficult” living conditions when they lived with Sinclair and another woman.

Hawaii News Now is not identifying the woman who filed for the TRO. In the petition, she writes there was domestic violence, fighting and drug activity in the home.

When they told Sinclair they were moving out, she alleges he said they were not allowed to leave and began harassing her partner about money.

The woman goes on to say that on June 5, her partner called her to say he was leaving work, but never made it home. She says she went to his workplace, where she reportedly found him dead.

“Out of respect right now for the owners of the establishment, we’re not going to reveal the location,” Kauai Police Department Assistant Chief Darren Rose said in a news conference Monday.

After his arrest in the ocean near Kapa’a Beach Park on Monday morning, KPD confirmed there was a financial dispute between Sinclair and the victim, whose identity has not yet been publicly released.

“Not to jeopardize the investigation, I’ve got no details on what the dispute was about, but it was not over drugs or anything criminal,” Rose said.

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Police confirmed Sinclair had no criminal history in Hawaii but is a convicted felon in California, with convictions for destroying or concealing evidence, participating in a criminal street gang, obstructing public officers and firearms offenses.

“We’re still reviewing all of that but from my understanding, there is some active TROs here on island potentially with his neighbors,” Rose added.

Court records show two other TROs were granted in 2025.

A neighbor wrote that Sinclair came to his home on two occasions — once swinging a large knife and another time threatening him with a gun while saying, “Get out of my house. Get on the ground.”

The second TRO was filed in December by another neighbor who said disputes over dogs escalated to violent threats, racial slurs, intimidation and harassment.

Kauai residents said they are relieved Sinclair is now behind bars.

“I think everyone’s just spent, a little bit at ease. It’s a very peaceful place. People are back to normal now,” Kauai resident and witness to the arrest Raymond Harrison said.

At last check, police said next-of-kin notification is still pending for the victim. Details on formal charges are also forthcoming as the investigation remains active.

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