During the December holiday rush at Tyrone Square Mall, William Deparvine stopped at Dairy Queen and bought an ice cream.
He sat on a bench and scooped the Blizzard into his mouth while St. Petersburg police Detective Mike Britton watched anxiously from 50 feet away.
Britton had trailed Deparvine for weeks searching for forensic evidence. He shadowed him from work. He watched as he did laundry. He followed Deparvine to dinner.
Deparvine finished the dessert and tossed the cup and spoon into a trash can.
"I have to get the spoon," Britton said to himself.
On it authorities found the DNA they needed to link Deparvine to the November deaths of Richard and Karla Van Dusen of Tierra Verde.
The genetic fingerprint in Deparvine's saliva matched blood on the steering wheel of the Van Dusens' abandoned Jeep Cherokee, court records say. Deparvine, 51, killed the couple Nov. 25 in Tampa while negotiating the sale of their 1971 restored Chevrolet truck, detectives say.
"It provides direct evidence to what was an entirely circumstantial case," Bruce Bartlett, chief assistant state attorney for Pinellas and Pasco counties, said of the DNA.
On Thursday, a judge in Hillsborough County ordered Deparvine to provide another DNA sample. The sample collected from the ice cream spoon was not in perfect condition, and prosecutors wanted a solid case.
Deparvine's Jan. 13 arrest has also reopened investigations into six unsolved killings in the 1980s in Texas, Sarasota, Clearwater and St. Petersburg. Deparvine was a suspect in 1992 in several of those cases, but detectives say they lacked witnesses and physical evidence to charge him.
"Often, you know who's responsible, but knowing it and being able to prove it are two different things," Sarasota County sheriff's Capt. Dario Valente said this week. "In our world, you have to be able to prove it."
A day after Deparvine met with the Van Dusens to finalize the purchase of their truck, their bodies were found on a dirt driveway in Tampa. Richard Van Dusen died of a gunshot wound. His wife had been shot and stabbed.
The Florida Department of Law Enforcement analyzed blood from the Van Dusens' Jeep, abandoned a mile from their bodies. DNA testing showed a mixture of Deparvine's and Richard Van Dusen's blood, court records say.
Hillsborough County investigators asked Deparvine for a DNA sample.
Investigators turned to the St. Petersburg Police Department's special investigations unit.
Britton, the St. Petersburg detective, was handed a picture of Deparvine and addresses for his work and downtown St. Petersburg apartment.
The mission: Get saliva and acquaintances.
From the end of November to about New Year's Day, Britton and several detectives spied on Deparvine by foot and car, trailing him to Best Buy and his movements on buses, his only mode of transportation.
St. Petersburg detectives camped out at strategic locations with a bird's eye view of the courtyard at Deparvine's apartment complex. They even dug in a Dumpster and sent Hillsborough investigators two trash bags Deparvine deposited.
Weekdays, Britton picked up the trail at 3:30 p.m. when Deparvine got off his construction job. He and other detectives followed Deparvine to his apartment, where he vanished into his unit. Detectives watched until Deparvine's bathroom went dark, usually about 10 p.m. when he went to bed.
"He was about the most boring person you could work," said Britton, who retires today after 28 years with the Police Department. "I think his life consisted of doing laundry at night a couple of times a week, and basically he never came out."
During one surveillance, plain clothes detectives swooped in and snatched up an Arizona tea bottle Deparvine discarded at his construction job in Clearwater. The bottle was sent to Hillsborough investigators. Britton never heard if any DNA was recovered from it.
Deparvine was a loner, Britton said. Occasionally, he chatted with neighbors, but he did not socialize or go to bars.
One time, Deparvine went to Shells restaurant on Fourth Street with a woman who detectives believe was his ex-wife, who lives in Ellenton.
For the most part, Deparvine's weekend activities consisted of taking a bus from Williams Park in downtown St. Petersburg to Tyrone Square Mall.
On Dec. 20, Deparvine rode a bus to the mall, which was packed with holiday shoppers.
He returned a coffee maker at JCPenney, then visited Dairy Queen.
Britton, dressed in jeans and a T-shirt, dug into the trash, dropped Deparvine's spoon in a bag and kept following.
Deparvine walked to a gum machine and bought a big, purple gum ball and popped it in his mouth.
"He got the mother of all DNA and put that in his mouth," Britton said. "He kept that gum in his mouth. We were watching him chew it the whole time he was at Burdines and Sears."
Deparvine bought dishes or pots and pans at Burdines, Britton said. Then Deparvine purchased a toy cordless drill at Sears. The box said, "My first tool."
Deparvine wasn't chewing the gum when he left Sears, Britton said.
"It's in the parking lot somewhere."
Leanora Minai can be reached at minaisptimes.com or (727) 893-8406.
Tracking the DNA
November-New Year's: Detective Mike Britton and other detectives trail Deparvine.
Dec. 20: Deparvine eats a Dairy Queen Blizzard at Tyrone Square Mall. Britton retrieves the spoon from the trash.
Jan. 13: Deparvine is arrested.