Honolulu Fire Department investigators maintain that a pre-dawn fire Thursday that caused extensive damage to a vacant city beach house at Waimanalo Bay Beach Park was intentionally set, and have turned the case over to police.

Among the suspicious circumstances tied to the fire were a gasoline can found at the scene as well as witness reports of hearing voices and a car speeding off, HFD Capt. David Jenkins said.

The house, at 41-1055 Kalanianaole Highway, was the scene of the July 5, 2014, fatal stabbing of 52-year-old Jolyn Kipapa, allegedly by her then-16-year-old adopted son.

On Thursday firefighters responded to an alarm at 3:40 a.m. and arrived at the scene seven minutes later. They found the two-story home engulfed in flames, Jenkins said.

Seven fire companies with 26 firefighters brought the blaze under control at 4:03 a.m., and it was fully extinguished at 6:09 a.m., according to the Fire Department.

The house was unoccupied and no one was injured, Jenkins said. It is considered a total loss with an estimated value of $300,000.

A city official said the home has been vacant since Dec. 1 due to an ongoing refurbishment project, which had been scheduled to be completed by late spring.

Kurt Kipapa, the former caretaker who lived in the home, is the widower of Jolyn Kipapa. He no longer works for the city Department of Parks and Recreation, which is assessing the damage and whether the structure can be salvaged.

Ka‘anoi Kipapa, charged with murdering his adoptive mother, remains in custody at the Kapolei Youth Detention facility, unable to post $250,000 bail. The Family Court waived jurisdiction on Oct. 30, 2014, allowing the Waimanalo teen to be tried as an adult.

Kipapa faces a hearing next month to determine whether he is fit to stand trial.

Park visitors say they were stunned by the news of the fire.

“I was shocked when I came here,” said a 52-year-old Waimanalo woman who declined to give her name.

The woman said she used to camp every weekend at city campsites and got to know Jolyn Kipapa, who was “really nice,” and the adopted children, including the suspect. “It used to be a good place to camp until that happened,” she said, referring to the murder.

Regarding the fire, she said, “Why would they do that? Looked like they went upstairs because downstairs is not burnt.”

While the lower portion of the house, including large posts, storage areas and a stairway were untouched by fire, the blaze burned through the roof and blackened the entire second story.

Former Waimanalo residents Josh and Maile Dang, 38 and 44 respectively, who now live in Hauula, said they found out about the fire on the morning news.

“The first thing we wondered about was the kids — was everybody OK?” said Josh Dang. “About a month ago they were still here.”

Maile Dang said, “We were shocked. Every time we stop here, we always see the house.”

The couple said they were married at the beach and that it’s their special place.