Like many children her age, Kym Willis, 14, is a big fan of television shows that revolve around crime-solving. Willis particularly likes Bones, about a forensic anthropologist, and Rizzoli and Isles, which follows a detective and a medical examiner on the job.

In fact, Willis said, she might like to work as a medical examiner one day.

"I want to do the autopsies," she said.

Philadelphia Police Commissioner Charles H. Ramsey hopes more students like Willis will translate their interest in crime shows into careers in forensic science when they enter college.

Ramsey and members of the Police Department's forensic science bureau hosted an informal class Thursday for about 50 Delaware County students, including Willis, to show how technological advances help police solve crimes.

The students, from St. Gabriel's School in Norwood, spent the morning visiting the Franklin Institute's "CSI: The Experience" exhibit, then hearing from Ramsey and other officers about how they investigate crimes. They also toured the Philadelphia Police Department's mobile crime unit, a van equipped with all the tools investigators need to process a scene.

"This is a way to show kids that they can work alongside officers, as part of the Police Department, without actually wearing the uniform," Ramsey said. "There are a lot of different careers out there for students who are interested in science."

While exploring the exhibit, students studied fake crime scene photos and looked for clues, matched tire treads and DNA, and compared charts that displayed various blood-alcohol level readings.

Mike Garvey, director of the forensic science bureau, was on hand to answer questions and offered students a few examples of how actual crime-solving differs from the way it is portrayed on TV. For one thing, he said, the same person is rarely able to analyze all types of evidence collected at the scene - investigations require teamwork.

"Everyone knows about different things and has different expertise," he told the group. "It's only when you combine all your resources that you get what you see here."

After touring the exhibit, several students had questions for Ramsey, Garvey, and the other officers in attendance.

"How many crimes do you solve in one week?" asked one boy, prompting Ramsey to explain that while the investigators solve some crimes within hours, others take years. Overall, he said, the department solves more than two-thirds of the city's homicides.

"It depends on what you have as far as evidence," he said. "The key is to process every scene very carefully, so we can gather as much information as possible."

Sometimes, Garvey explained, investigators don't know what will be important in solving a case. DNA evidence that leads to no one might end up matching someone years later, for instance. Police depend on those who work in labs to help them fully analyze each piece of evidence, he said, whether it's a DNA sample, a hair, or something smaller.

When another student asked how police solve crimes if there is no evidence, Ramsey and Garvey detailed some of the ways police search for signs of evidence even if there appears to be none: dusting for fingerprints, looking for eyewitnesses, scouring the area for possible video surveillance, and talking to people who were familiar with where the crime took place.

"With every case, you don't know what evidence will be there," Garvey said. "TV tells you that if you don't have DNA evidence, it'll be a bad case, but that's not true. Science has given us all kinds of other ways of collecting information."