Keeping track of traces

~ Police have to work quickly to record the evidence at a crime scene.

The evidence is everywhere.

A dot of blood on the floor, a hair follicle on the windowsill, skin cells under fingernails.

It's DNA, and you leave it wherever you go.

"Whenever people walk into rooms, you're dropping hairs, you're dropping skin cells," said Cape Girardeau police Cpl. Joseph Tado. "That puts the person at the crime scene."

Tado is a detective for the police department's Scientific Investigation Unit and the lead crime scene investigator for Bollinger and Cape Girardeau counties' major case squad. It's his job to hunt for and find trace amounts of evidence from a crime scene, whether it be a fingerprint or an eyelash.

What struck this doorknob? To find out, investigators make a cast. First, the casting material is mixed, top left. Then it's applied to the doorknob, top right. After it hardens, the mold is then carefully pulled off, bottom left. The result, bottom right, is the cast of the marks. (Diane L. Wilson)

Crime scene investigators work under one general principle: If two objects touch, they exchange particles. It is that exchange investigators look for, something a suspect left at or took from a crime scene.

Because officers who enter a room can alter the area from their own skin cells falling off, evidence technicians have to work quickly and accurately.

"You lose probably 70 percent of trace evidence within the first couple of hours of a crime happening," Tado said.

He noted that whenever investigators enter a crime scene, they always put their hands into their pockets to deter them from absentmindedly touching something and contaminating it.

To help with the preservation of a crime scene, investigators can wear Tyvek suits, which cover them head to toe to keep their DNA in and other material -- including hazardous biological material -- out.

Tado said crime scene investigators are using Tyvek suits more and more for those two reasons.

"Eventually you will see it will be standard practice, probably nationally, that any homicide will be Tyveked up," he said.

When officers first arrive at a crime scene, they secure it and call their supervisors, who then contact detectives. Arriving evidence technicians then document everything at the scene, Tado said. Photographs are taken, notes are written, precise measurements are made, all to allow detectives to recreate the scene in the future.

Distances from a body on the ground to a weapon, wall, chair or other materials are measured.

"You cannot go back into a crime scene three years down the road," Tado said. "What you want to do is to be able to put that body back to exactly where it was 20 years later."

In addition to rulers and tape measures, investigators also use black lights to detect various fluids at a scene unnoticeable to the naked eye, and use transparent, sticky sheets to collect dust and hair particles to be analyzed later.

In some instances, technicians can more reliably collect DNA than fingerprints at a scene, Tado said.

"DNA is extremely accurate," he said. "Now they're having more success obtaining DNA off the firearm than they are latent fingerprints. That's how advanced DNA is."

It has not always been that way.

In the Cape Girardeau Police Department's first DNA case 14 years ago, a woman awoke to find a man standing over her. He covered the woman's mouth with his hand and raised a knife that cut his face, according to Prosecuting Attorney Morley Swingle.

The man fled, leaving behind blood. That blood proved a match with the man who later was charged with burglary, assault and armed criminal action.

Unfortunately, when the case was tried in 1992 DNA evidence was still new to the public, Swingle said.

The defendant, who represented himself in court, was able to sway the jury against the "mumbo jumbo" DNA evidence and convince them he never did anything, despite his blood being at the scene, Swingle said.

"Nowadays it'd be a slam-dunk," he said.

With both technology and public knowledge of DNA improving over the last decade, an offender can now be convicted with only a hair follicle link to a scene.

Last May, a jury convicted former Columbia, Mo., police officer Steven Rios of first-degree murder and armed criminal action in the June 2004 slaying of his 23-year-old gay lover, Jesse Valencia. Key evidence from the scene included DNA recovered from under the victim's fingernails and hair found on his chest, all of which matched Rios.

Logic may be as important as DNA evidence when investigating scenes, Tado said.

"When you talk about forensics, everybody loves to talk about the cool stuff," he said. "But they overlook the common-sense area."

For example, when investigating the apparent heat-related deaths of an elderly woman and her son last summer in Cape Girardeau, investigators attempted to determine when they had died. The two had a newspaper subscription and regularly brought the paper inside their home, Tado said. Four newspapers lay outside their door, so Tado could tell they had been dead for four days.

kmorrison@semissourian.com

335-6611, extension 127