Chapter 7. Old applications of fingerprint technology
Theodore carefully removed Bernie's cup from the evidence bag, wiping it thoroughly with his shirt before walking toward Brian's house.
He rang the doorbell, and the door opened just a crack, revealing Sitt's wary face.
"Oh, it's Officer Dickson and Officer Sullivan," he said loudly, his voice carrying an odd forced cheer. "Is there something you need?"
Theodore frowned. "Is Anna home? We have a few questions for her."
It was natural for residents to become vigilant after a brutal family massacre in their community, but being this guarded when police knocked on the door crossed into suspicious territory.
Bernie wasn't dense—he also sensed Sitt's strange behavior. His hand drifted to his gun holster as he pulled Theodore behind him and forcefully pushed the door open.
"Go get Anna. We need to ask her some questions. It's not just your house—all residents here need to be interviewed. Move it, don't waste our time."
Bernie's impatience was genuine now.
He was already intimidating by nature—broad-shouldered and stern-faced—so he didn't need to put on an act. A simple scowl was enough to make most people comply.
Sitt froze in place, his face draining of color. He stammered, about to speak, when a voice from behind stopped him.
"Sitt."
Anna appeared, forcing a smile as she smoothed her apron. "Come in, please. I heard about what happened to them—is it really true? It's simply terrifying." She gestured them inside. "Ask whatever questions you have. I'll cooperate fully."
She gave Sitt a gentle push. "Sitt."
Sitt startled, as if waking from a trance, and looked at Anna with confusion.
Anna smiled warmly at him. "Sitt, go to the kitchen and bring some cake for our guests."
After sending Sitt away, she explained to Theodore and Bernie, "It's my mother's recipe. I baked it last night—you're welcome to try some."
Theodore tilted his head, studying her. "Aren't you going to ask how the investigation into your mother's case is progressing?"
Anna blinked. "How is the investigation going?"
"There's been a major breakthrough, but I can't share details yet," Theodore replied with a slight smile. His gaze dropped to Anna's bandaged hand. "What happened there?"
Anna seemed flustered, instinctively hiding her hand behind her back. "Oh, this? I accidentally cut myself with a knife. We were planning to celebrate with steak last night, and I slipped while slicing it."
Theodore nodded noncommittally. He slid Bernie's cup across the coffee table. "We've been working outside for a while and got pretty thirsty. Could you pour me some water?"
Anna picked up the cup somewhat absently, filling it only halfway.
Theodore lifted the cup and drained it in one go, then immediately slipped it into an evidence bag. He stood up with apparent impatience. "Thank you for the water. That really helped."
Just like that—in and out in minutes. Bernie was completely bewildered as Theodore hurried them back to the car, constantly urging him to drive faster.
Back at the police station, dusk was settling over the city. The Homicide Team office buzzed with even more activity than when they'd left—five hours had brought a steady stream of new information.
Theodore didn't disturb the others. He instructed Bernie to gather tape, pencils, and gauze while he headed to the forensic lab.
The forensic examiner was still working on Diane and Doyle's bodies. Porcelain Plate and Mrs. Brian would have to wait—according to Homicide Team protocol, new cases claimed priority for all resources.
Fortunately, the fingerprints Theodore had repeatedly emphasized that afternoon were ready. They were complete and remarkably clear, which genuinely surprised him. He gave the old forensic examiner an appreciative thumbs-up and hurried out with the fingerprint cards.
When he returned to the main office, Bernie had assembled the requested materials and sat waiting. Seeing Theodore's approach, he asked urgently, "What exactly are you planning to do?"
"Mr. Wenner wants evidence," Theodore said, his excitement barely contained as he gathered the bags and supplies. "I'm about to give him exactly that."
He rushed into the supervisor's office, startling Wenner.
"What's the emergency?" Wenner asked.
Theodore didn't answer immediately, instead instructing Bernie to start sharpening pencil leads. Wenner looked to Bernie, who appeared equally confused but complied anyway.
Once there was a small pile of graphite shavings, Theodore had Bernie crush them into fine powder. He pulled on gloves, removed the cup from its evidence bag, wrapped the graphite powder in gauze, and held it seven or eight inches above the cup's surface.
He glanced up at Wenner. "Are you familiar with fingerprint extraction and comparison technology?"
Without waiting for an answer, Theodore carefully shook his wrist. Fine graphite powder drifted down like dark snow onto the cup's surface.
At first, nothing seemed to happen. But gradually, as more powder settled, it appeared as though a thin black veil had been drawn across the cup.
Theodore stopped dusting, rotated the cup to catch the light, and blew three short, controlled breaths. A small fan-shaped area of carbon powder scattered away, revealing the underlying surface now coated with fine graphite particles that had adhered to invisible residue, forming delicate ridge patterns.
Theodore exhaled slowly, set down the cup, and cut a section of tape. With practiced precision, he pressed it carefully against one side of the revealed print.
Only then did Wenner speak. "I'm familiar with fingerprint technology. Currently, all states are cooperating with the FBI to establish comprehensive databases, but they're far from complete. The FBI's database contains only tens of millions of prints. Do you know how many people live in the United States today?"
He answered his own question. "Two hundred million!"
"But only tens of millions of fingerprints are on file. To search for one print among tens of millions, and then hope it's actually in that database—do you understand those odds?"
Since the 1930s, the FBI had employed fingerprint technology, and the first director, J. Edgar Hoover, had systematically pushed his agents to collect and build extensive fingerprint databases.
However, due to technological limitations, fingerprint comparison in this era required trained personnel to examine fingerprint cards with magnifying glasses, manually comparing characteristic points. At least ten matching points were necessary to confirm a positive identification.
This was time-consuming, labor-intensive, eye-straining, and expensive work. Although fingerprint technology had existed for decades, 99.99% of cases simply couldn't justify the cost of using it.
From a conventional perspective, Wenner was absolutely right. Even if the Homicide Team spent their entire annual budget, it might not cover the expense of processing a single set of prints.
But all of this assumed a one-to-many comparison—searching an unknown print against vast databases.
What about a one-to-one comparison?
What if you had a target print for direct comparison?
Theodore nodded, angling the cup away to prevent contamination from Wenner's breath. "But what if we only need to verify the identity of one specific set of prints?"
Wenner opened his mouth, then seemed to abandon whatever argument he'd planned.
Theodore didn't pursue the point. Once the tape had captured all the ridge patterns, he pressed it repeatedly to ensure good contact, then carefully peeled it off and transferred it to a blank fingerprint card.
The improvised tools produced prints that weren't as sharp as those extracted by the forensic examiner's professional equipment, but they were more than adequate for targeted comparison.
Theodore pulled the desk lamp closer, switched it on, and began methodically comparing his extracted prints with the cards from the forensic lab, narrating his process:
"These are the prints the forensic lab lifted from the murder weapon—they're exceptionally clear. The ones on the cup belong to Anna."