As the bags of cocaine and crack changed hands, some students were mesmerized by the fine white powder and others stopped to roll the waxy chunks beneath their fingers. For most, it was the closest they had ever come to a street drug, and the denim-clad man at the front of the room was talking about the power within the plastic bags and the dangers.

"Think of the best time you've ever had in your life, and double it," said Detective Ross Randlett, jumping up onto a table to demonstrate how high some people say they feel when using cocaine. "Cocaine has one really bad thing about it, though. You get double the low."

Randlett, wearing a black motorcycle shirt, denim jacket, blue jeans and a pair of steel-toe boots, was explaining to the members of the county's Citizens Police Academy how he moves through the dregs of Prince William society on a mission to get such drugs off the street.

A member of the Prince William County Police Department's Vice and Narcotics Unit, Randlett spoke last week about befriending the bad guys to get to more bad guys, about the never-ending string of drug pushers and about the 18-hour days he sometimes spends hunting down those who poison the county's youth as they seek money and power.

"We have to get down in the gutter; we have to deal with these dirt bags every day," Randlett said, looking far more the part of biker than cop. "These guys are extremely smart, these kids are extremely smart. We'd be a lot better off if they would only put it to a constructive use."

Randlett's explanation of the science of narcotics caught the attention of the class, which is entering its third week of the academy's 12-week program. Robert Hornby, of Manassas, was especially interested in the simplicity of converting powder cocaine to crack cocaine; Randlett explained how easily dealers can double or even triple their profits by doing so.

"These guys have it down to a science," Randlett said, a smile growing. "It is really cool to see how they do it; it's really wicked. But is it illegal? Yep. Do we lock them up? Yep."

In just the first three weeks of class, members of the public have been exposed to a wide array of components of the police department, from internal affairs investigations to recruitment, accreditation and crime analysis. The broad-based course narrowed to specific instruction on individual units in the second week, covering, among other topics, the use of polygraph machines, which made for a popular discussion among class members.

Frank Myers, one of the department's two full-time polygraphers, explained that the use of polygraph is mostly limited to testing applicants for police department positions. Myers said that each applicant is thoroughly tested to ensure that the people hired are honest, especially about their past drug use or illegal activity.

Myers said that contrary to much of the public's perception, a polygraph machine is not in fact a "lie detector." He said that if a polygraph administrator does not know the right questions to ask, the test's results will not give an accurate picture of the truth, or anything else.

"There is no such thing in this world that is a lie detector," Myers said, leaning over an older-model polygraph he was displaying to the class. "My duty is to verify the truth. The polygraph machine only records what an individual believes to be true. It is only an investigative aid, just a part of the overall investigation."

The polygraph literally means "many writings," and it tests for a variety of physiological changes that occur involuntarily when someone is caught in a lie. Myers equated the internal nervous system changes to the feeling some speeding drivers may have when cresting a hill on the highway and then noticing a police car on the other side.

"You can feel something rise in your chest, and your heart might feel like it's racing," Myers said. "Those are things you can't control, and that's what we're looking for."

The machine records changes in blood pressure, electrical shifts in the body and the tightness of the skin, all elements that people cannot control. Myers said it is virtually impossible to "beat" a polygraph test, which is comprised solely of yes-or-no questions. Even a slight variance within the body is meticulously recorded.

He said that one of the major limitations on the use of polygraph as a crime fighting tool is that the law requires consent from the person being tested and that test results are generally not admissible in a courtroom. In 1999, the police department administered 494 polygraph tests and only 74 of those were used for criminal investigations.

Andrea Hoard, a police recruiter, said that the polygraph is an essential piece of the recruiting puzzle and that often it is the deciding factor in narrowing the application pool. Hoard said the department receives nearly 600 applications for each Police Academy entering class of 25.

Because the department is looking for the "highest quality" applicants, there is rigorous testing and evaluation before someone is even admitted to the academy, and even then there is no guarantee of being sworn in as an officer, she said.

Hoard said that as the department has grown and the demographics of Prince William have changed, the agency has been expanding its reach to different people, such as those with computer degrees and advanced liberal arts degrees, to keep up with the kinds of crime the department is seeing. "With changes in crime, we have to see a different type of officer," Hoard said.

And the department has widened its search because of its need to diversify both in ethnicity and in specialties, especially because of competition with other Northern Virginia agencies. Still, standards remain high regardless of how many new officers the department needs, she said.

"We are still probably one of the hardest police departments to get into in the area," Hoard said.

Staff writer Josh White is attending the Citizens Police Academy. His reports will appear every other week.