CLEARWATER

At first, Mark Smith called every few days.

Days turned into weeks. Weeks turned into months. Months turned into years. The calls to the Pinellas County Sheriff's Office became fewer and seemed more fruitless.

Today marks 25 years to the day that Smith's brother Gary and sister-in-law Sally were killed in their home. It is the Sheriff's Office's only unsolved double murder.

Though his hope for a breakthrough faded, Smith's calls from Stockton, Calif., never completely stopped. He kept a log of the roughly 50 he made through the years.

"Asked if there was any progress," he jotted down in 1992. "No, and no new leads."

"Case at a standstill," he wrote six years later.

In 2012, he talked to detectives twice. "No new developments," Smith, 71, noted.

But this year, he got some promising news.

• • •

The oldest of three brothers, Richard Gary Smith was born and raised in Stockton. His father was an electrician and a contractor. He pursued the same careers.

In the 1980s, Smith, who went by Gary, traveled to Florida to work at a construction project. He stayed and started his own company, Design Electric at 11620 54th St. N. When Smith wasn't working, he was scuba diving, boating, or camping with his sons, Cole and Mitchell, when they visited from California.

Gary met Sally at a Clearwater bank, where she worked as a teller.

"They seemed to hit it off," Mark Smith said. "She was very kind to him that I could see, and he really loved her."

They married in 1986.

Born in Milwaukee, Sally was close to her sisters and brothers, smiled often and loved to sing, at one point recording several songs with a sister. She held different jobs through the years, including as a real estate agent and clerk at Morton Plant Hospital's radiology department, where she met best friend Kathi Terpin.

"Very few people are fortunate enough to find one truly good friend in life,'' Terpin said. "And I think she was that friend."

When Terpin had a son, Sally came with gifts — a car seat, a baby swing and toys.

"It was like Christmas," Terpin recalled. "She had purchased so many presents for him. She just kept bringing them in from the car."

Sally sometimes talked about having kids of her own.

The Smiths occasionally held beach parties with plenty of beer and sandwiches. They invited friends and Design Electric employees.

"They were so well-liked by everybody," said neighbor Marie Gibson. "He was just a good person. Sally was just as sweet as could be."

On the night of Sept. 4, 1989, Gibson and her husband, Jack, stepped outside to crime scene tape and flashing police lights in front of the Smiths' home on Drew Street.

• • •

Sally's brother discovered the bodies when the Smiths didn't show up to a family gathering.

Gary, 50, was shot twice and stabbed in his stomach. Sally, 35, was strangled. Detectives believe they died three days earlier, on Sept. 1, after Gary left work to watch a movie with Sally.

Detectives determined the Smiths were targeted. There was no forced entry, though the back sliding glass door was likely shattered during a struggle. Unidentified fingerprints were found inside.

The Sheriff's Office early on suspected that money owed may be the motive. Design Electric had faced some financial challenges.

A supplier sued the company in November 1988 for failing to pay $17,869. In a letter to the supplier, Smith said he had agreed to pay $250 monthly and vowed to pay more "when and if my then very precarious business position was stabilized," adding that someone owed him $27,000. In 1989, he took out a $20,000 loan, the Tampa Bay Times reported in 1994.

"The economy started to take a dip," Mark Smith said, "and he was really trying hard to keep it going."

Six years passed and no arrests were made. Ten billboards announcing a $33,000 reward offered by family and friends were erected throughout Pinellas.

Detectives received several tips, but nothing of substance.

"There's no sense of closure until you find out why or who or what happened," Terpin said.

• • •

The Smiths' murders are among 37 unsolved homicides on the Sheriff's Office books.

Many cases have little to no physical evidence. But the Smiths' case has about 100 items, which Det. Michael Bailey calls "promising."

"There's a good chance that it could be solved," said Bailey, who was previously assigned to the investigation. "There actually is some forensic evidence that will be pursued."

Detectives are doing that now: the Smith investigation got some traction in 2012 when the Sheriff's Office received a grant to further investigate cold cases. They sent evidence from several murders for DNA analysis and digitized tattered police reports from older files.

Evidence from the Smiths' case was submitted, but detectives declined to discuss the results.

Money could still be the motive, but investigators are keeping an open mind, said Lt. Michael Holbrook, who oversees the homicide unit.

The Sheriff's Office has not named any suspects since 2004 when detectives focused their attention on William J. Deparvine, accused of killing a Tierra Verde couple during the sale of a red 1971 Chevrolet Cheyenne. Deparvine, 62, was convicted in 2005 and sits on death row.

"I couldn't say we're actively seeking him as a suspect," Holbrook said, "but he has not been ruled out."

There are similarities in the cases: a red Nissan was listed for sale in the Smiths' front yard. Deparvine worked in a Tierra Verde construction project where Gary Smith also worked, but it's unclear if the two ever met.

For Mark Smith, attaining justice for his brother and sister-in-law is a desire that has not dulled through the years. He hopes the latest look at the evidence provides answers.

"This is coming to a last shot at it."

Times staff researcher Natalie A. Watson contributed to this report. Contact Laura C. Morel at lmorel@tampabay.com or (727)445-4157. On Twitter: @lauracmorel.