After using video cameras to track the movements of Allen D. Wade Jr. in the hours after police believe he killed two sisters in East Liberty, investigators are now working on a number of fronts to bolster their case on the microscopic level.
In an affidavit supporting the arrest Wednesday of Wade, 43, for the killings of Sarah and Susan Wolfe, his next-door neighbors on Chislett Street, police wrote that there was a mixture of DNA from a male and female under Susan Wolfe's fingernails.
Wade, the affidavit said, "cannot be excluded as contributor to this mixture," according to the Allegheny County medical examiner's forensic laboratory division.
Neither the county crime lab nor the district attorney's office would expand on that statement.
Wade said he is innocent.
It could be telling that Pittsburgh police have retained a local company, Cybergenetics, that specializes in analyzing DNA mixtures from more than one person, to run the evidence through its TrueAllele computer analysis.
The analysis, pioneered by Cybergenetics in Oakland, has been used in various hard-to-solve cases. It can take mixtures of DNA and conclusively identify -- or exclude -- a suspect, and do so more reliably than older DNA technology.
The phrase "cannot be excluded" appears often in criminal cases and hints to defense attorneys that they might have an opening to raise questions about the quality of the DNA match, veteran defense attorney Patrick Thomassey said.
"That tells me that it's a mixture of things and I don't think it's that strong," said Mr. Thomassey, who estimated that he has worked on about 100 cases involving DNA evidence but is not involved with the Wolfe case. "That 'cannot be excluded' phrase is troublesome to the district attorney."
Investigators also have submitted for DNA analysis a hat found inside the home of the Wolfe sisters during an unsolved December burglary in which two televisions were stolen.
As well, detectives took a DNA sample Wednesday night at police headquarters from a man who knows Wade and who they questioned in connection with the Wolfe case, according to a law enforcement source familiar with the investigation.
In addition to having the DNA results from Susan Wolfe's fingernails as evidence, detectives learned that a blood stain on a pair of gray sweatpants -- which they say is linked to both Wade and Susan Wolfe -- contained Wade's blood, the affidavit said.
The match was made between the blood stain and a DNA profile of Wade on file with Pennsylvania State Police since a robbery conviction years ago.
Janine Yelenovsky, the county forensic division's laboratory manager, would not say when the lab asked state police to run the genetic profile isolated from the blood stain against the state's DNA database, which contains about 300,000 profiles.
But police found the sweatpants Feb. 8, the day after the sisters' bodies were discovered in their basement, and DNA results came back Monday, according to the police affidavit.
Ms. Yelenovsky confirmed that her lab had asked state police to expedite the DNA search, which typically can take more than a month from the point when the evidence sample is obtained to when the state police lab is done running through its protocols and can release the name of a suspect to investigators.
For a generation spoiled by fictional crime-scene science on TV, it is sometimes hard to remember that real-life investigators do not move at the same speed as Hollywood.
"It's definitely not CSI -- before the commercial break they send it for DNA and when the two-minute commercial break is over they have the profile and they're out looking for the guy," said Michael Biondi, DNA quality assurance program manager for the state police Forensic DNA Division.
That said, in a perfect world, a sample of genetic material from a crime scene in Allegheny County could theoretically yield a suspect in as little as a week.
But that's assuming state police, which often work hand-in-hand with local police departments and the county's crime lab, fast-track a case.
DNA samples can come from blood, semen and saliva. They can also be obtained from something called "touch DNA" -- DNA obtained from skin cells left behind on, say, the grip of a gun.
Analysts first screen samples using a microscope or chemical test. Is that red-brown stain actually blood? Is the material on a vaginal swab semen?
Screening can typically be done in minutes or hours. Only one such test runs overnight.
Next, lab techs isolate stains from the material through taking swabs or cutting a swatch.
Samples are separated by type -- blood and saliva placed together in one box, semen samples in another -- and then placed individually into wells of a small plastic tray.
Analysts typically wait until the particular tray is filled with between 30 and 50 samples before DNA analysis is performed. But they can choose to run tests earlier.
Ms. Yelenovsky said investigators try to balance the need to process evidence quickly with concerns that doing so before the disposable tray is full could be a waste of resources.
The next step is to isolate the DNA, which takes two to three days. The data is examined and compared to victims, suspects and people who police are trying to rule out. That could take several hours.
If the DNA profile isolated by the crime lab meets certain criteria, it is uploaded into the state police database. That upload happens once a week. In turn, the state uploads to the FBI's DNA database, the National DNA Index System, which is part of the Combined DNA Index System (CODIS). Once a week the system tries to match the profiles it has received to known offenders.
"You come in the next week after the database is searching over the weekend and you come in Monday morning and the CODIS software provides you with potential matches," Ms. Yelenovsky said.
Anyone convicted of a felony in Pennsylvania must provide a DNA sample to be entered into the state database. The lab in Greensburg stores them.
Screening DNA occurs as samples come in. If there is a threat to public safety, Mr. Biondi said, the state police will "pull them out of rank."
"We do try to prioritize homicides, rapes, any cases that involve a juvenile," Mr. Biondi said. If not expedited, cases will be assigned within 30 days of when they are received, he said.
Once a case is assigned it typically takes two to four weeks before a DNA sample is isolated, compared and written up in a report. A turnaround of several days is possible, but that does not happen often.
If a match is made, there is another delay before the crime lab can notify the local law enforcement agency. A confirmation process is triggered that involves several steps and can take about a month.
Certain situations demand a shortcut. Instead of uploading the DNA profile to the state for inclusion in its database, the county can ask for a computer search "where they would send us the profile and we would go and keyboard search the profile against the database," Mr. Biondi said. "We have that same ability with the national DNA system."
That process takes all of half a minute.
Paula Reed Ward contributed. Jonathan D. Silver: email@example.com, 412-263-1962 or on Twitter @jsilverpg. Liz Navratil: firstname.lastname@example.org, 412-263-1438 or on Twitter @LizNavratil.