Over the course of two days, two women in Ross and another in Hopewell reported that a man they had never seen before had broken into their homes, held them at gunpoint and raped them.

The victims offered only rough physical descriptions of the assailant, and there were few witnesses. Ross police developed a suspect, whose car matched one seen leaving the scene of one attack, but their scant evidence linking him to the crime was not enough to charge him.

"There was no smoking gun," said Detective Brian Kohlhepp of the Ross Township Police Department.

But nine days later, police got just that: A link made through DNA found on the two victims in Ross matched the profile of 38-year-old Arthur Henderson, who had submitted a DNA sample after police obtained a warrant. He was in police custody within 12 hours.

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In spite of improvements in technology, DNA investigation remains a time-consuming and tedious process fraught with difficulties. The average turnaround at the Allegheny County Medical Examiner's Office lab for a crime scene sample was 313 days in December.

In this rape investigation, the seriousness of the case sped up the process, but the lab is beginning to work through a backlog and improve efficiency with new technology -- including a robot that can extract DNA many times faster than humans working manually.

Knowing they had "an active serial rapist on our hands," analysts prioritized the case, said Karl Williams, who heads the Allegheny County Medical Examiner's Office. Two analysts worked through the weekend processing samples to complete the analysis.

"It was crucial to the case," Detective Kohlhepp said. "Without the DNA evidence, we would have continued to investigate [but] we would not have had enough to charge him."

Their swift work may have prevented future attacks. A man matching his description was reported "acting suspiciously" in nearby communities, according to Detective Kohlhepp.

Mr. Henderson's family said he is innocent, said his attorney, Blaine Jones, who indicates he plans to have his own analysts examine the DNA evidence.

New equipment purchased with a series of grants will help the Allegheny County forensics analysts speed up work on many other cases, including more routine burglaries and years-old cold cases, laboratory manager Janine M. Yelenovsky said.

Key in the effort is the Biomek 3000, a robot that can extract DNA from as many as 60 samples in about two hours. The same work, done manually, would take weeks, Ms. Yelenovsky said.

Extracting the DNA is a bit like cooking -- you add ingredients, let them sit, shake them and let them sit some more.

Analysts use chemicals and other processes to strip away all other cellular material from a sample so all that remains is DNA. The process, done manually, takes up to 20.5 hours. The robot can extract DNA from a sample in about 21/2 hours and performs much of the labor, such as adding chemicals to the samples.

The robot was not used to process the DNA samples from the assaults in Ross, in part because each sample would have had to be segregated into its own tray. With a small number of samples, it's faster to process them manually.

But it will make rapid processing of high-priority samples possible and will speed processing of more routine samples.

That lengthy average time for processing crime scene samples is skewed by the fact that the lab has started testing samples from years-old cold cases, Ms. Yelenovsky said, but the forensic unit is actively working toward reducing turnaround time so it can be "ahead of the game."

The Biomek became operational in December 2010 and quickly revolutionized the extraction process for the laboratory. Lab statistics show each analyst processed, on average, a little more than 23 samples in December 2011, up from 3.8 samples per analyst in 2009.

Before the Biomek, the lab typically processed samples when they were associated with investigations that had already gone to court.

"With a court date you need a victim, an actor and a crime," Ms. Yelenovsky said.

But cases in which there was no suspects fell near the bottom of the stack. Her goal is to be able to give detectives leads in cases where there have been no arrests, instead of focusing solely on helping to convict defendants already on trial.

For detectives in Ross and Hopewell, the DNA evidence was the linchpin in the case.

"It was very important because we had no witnesses as to anything other than the victim statement," said Detective Greg Durkos of the Hopewell Township Police Department, adding that the victim could not make out her assailant's face because he was masked.

It was the first time in his 21-year career that DNA evidence helped him make an arrest.

The lab is already moving in that direction. In 2011, analysts entered 103 DNA profiles culled from crime scene samples into CODIS, a national database that aggregates profiles from hundreds of crime labs across the country and includes convicted offenders, missing people and other unknown profiles developed from crime scene samples. That's more than twice as many as in the previous year, when just 49 profiles were entered.

The DNA samples last year generated 15 "hits" in CODIS, meaning DNA profiles matched those of convicted offenders. Ms. Yelenovsky could not discuss the outcomes of those cases, saying many are now winding their way through the courts.

One of those hits was from a soda cup believed to be used by an armed robber in Ross. Detective Kohlhepp said the man came into a convenience store on Perry Highway on July 16, 2010, and was seen filling a cup from a soda fountain and drinking from the cup. He then robbed the cashier at gunpoint and left the cup behind.

The profile developed from the lip of the cup was uploaded into CODIS the following year and matched Daniel Litz, a convicted offender who is now in jail in Georgia on unrelated charges. Detective Kohlhepp said police are awaiting a confirmation sample from Mr. Litz to charge him in the crime.

"There was nothing to relate us to the offender. Had we not had DNA from the scene, that's a case I strongly believe would not have been solved," Detective Kohlhepp said.