As the sound of Independence Day celebrations and fireworks wound down early in the morning of July 5, 2013, Kelly Ann Boyce headed home with her bicycle. She was passing through a darkened neighborhood in Traverse City, Michigan, when she was struck from behind by a motorist and dragged more than a block to an alley before the motorist drove away, leaving her gravely injured.

She died shortly afterward at a nearby hospital, her husband at her side.

Three years have passed, and one of the most ambitious investigations ever undertaken by the Traverse City Police Department has failed to produce a suspect. It’s a grim reality that dismays members of Boyce’s family — including her mother, Michelle Boyce — as well as Traverse City police Capt. Jim Bussell, who answers phone calls from Michelle at least twice a month.

“I just assure her that we’re still working on this, that it’s still being investigated,” Bussell said. “Mostly, I listen, though.”

Michelle Boyce replays that fateful night over the phone as it reels through her mind. She sat in Kelly’s backyard two days after the hit-and-run. She watched detectives criss-cross the alley where Kelly was left to die. They canvassed the neighborhood, casting a net for witnesses and evidence, and it seemed to Boyce that the search would soon yield a suspect. But despite hundreds of tips that flooded their phone lines and email inboxes, police were unable to find a suspect.

To date, more than 30 city and Grand Traverse County detectives have worked on the case, joined by at least three local Michigan State police and three FBI agents. That’s not counting the numerous officers from other agencies who helped local police chase down far-flung leads.

Authorities have logged 767 tips to date and closed 93 percent of them. About 5 percent remain open, with another 2 percent awaiting a detective’s assignment. Special FBI-provided software allows Bussell to catalog and cross-reference tips.

Those requiring additional investigation yield supplemental reports. Detectives have filed more than 90 such reports.

Nicole Nostrandt, who is Michelle Boyce’s other daughter, said she finds it hard to accept that the motorist remains free.

“It’s just unbelievable that three years no one’s come forward and said what they know,” she told the Traverse City, Michigan Record-Eagle.

Bussell says the investigation remains frustrated by ambiguity in the information the police do receive.

“What would help us is if somebody came forward and said they believe this person is the individual and gave us some viable facts to support that,” Bussell said. “A lot of what we receive (are) assumptions and innuendo.”

Witnesses described spotting a dark SUV or pickup truck driving away from the crash. Tips about dark vehicles with front end damage comprised the bulk of leads detectives chased. But Bussell said an assumption the vehicle sustained damage could be false.

“There was no vehicle debris,” he said.

Bussell said nighttime tests conducted after Boyce’s death show any color, including white, could appear dark in that area. He said detectives still don’t know much about the vehicle itself, despite the witness accounts.

“We know it’s a vehicle,” he said. “We don’t know the size, the make, model or the color.”

Physical evidence comprised mostly of a long road mark leading to the alley and Boyce’s bicycle. Bussell said the bicycle sustained a single scuff mark on its tire. He said its chain hung loose, which indicates Boyce may have actually walked her bike along the street.

That and other information is cataloged in numerous spreadsheets saved on Bussell’s computer. They show an investigation of unprecedented scope for local police.

“We haven’t forgotten about the case,” Bussell said. “We’re still investigating as much as we can and we’ll continue to do that.”

The Traverse City, Michigan Record-Eagle contributed to this story.