“Your first priority is finding a secure place and a source of money,” said Darrin Giglio, chief investigator for the private agency North American Investigations. “You don’t want anything traceable, so you’ll either have to establish a new identity or get paid off the books, maybe as a day laborer.”

Frank Ahearn, author of “How to Disappear,” believes the key is found in disinformation.

“The idea is to combat the information you’re leaving behind,” Mr. Ahearn said. “I’d start by creating false data on your location, data and banking.”

Cellphone, credit cards, surveillance cameras and other products of modern technology have added new layers of complication and possibility for both fugitives and law enforcement.

“If they’re smart, fugitives can really take advantage of technology,” Mr. Ahearn said. “They can buy prepaid cellphones and credit cards. Their apartments, cars and bank accounts can be set up under anonymous corporations. They can live almost entirely virtually. That wasn’t possible in the past.”

To combat such trickery, police departments have access to increasingly sophisticated and far-reaching forms of search and surveillance.

“It’s easier than ever to comb through enormous amounts of data,” Mr. Giglio said. “And with surveillance cameras all over the place, the only way to avoid detection might be changing appearance. Some people even get plastic surgery.”

He added, “If fugitives ever slip up using technology or social media, they’ll get caught right away.”

And of course the fugitive life takes its toll.

“It’s like being in the witness protection program,” Mr. Giglio said. “To be successful, you have to give up your entire past. Most people can’t do that.”

Under such agonizing circumstances, there is no shortage of ways to blunder. According to Martin Horn, former commissioner of the New York City Department of Correction and a professor at John Jay College of Criminal Justice, escapees often return home or place phone calls to friends and family members, whom the police might be tracking. Other times it is an escapee’s suspicious behavior that tips off bystanders.

“A lot of inmates who are legitimately released encounter a confusing new life,” Mr. Pelz said. “They don’t know how to drive cars, use cellphones, use credit cards. They need to re-educate themselves. That can trip up escapees too. Even if it’s a well-planned escape, people get sloppy.”

Occasionally, fugitives are caught when they return to criminal activity. Mr. Welch was taken back to prison in 1980, after he shot Michael Halberstam, a cardiologist and the brother of the journalist David Halberstam, during an interrupted burglary. A bleeding Dr. Halberstam tried to drive himself to the hospital, but when he spotted his assailant fleeing down the street, he ran him down, wounding Mr. Welch before crashing the car.

Dr. Halberstam died on the operating table, but the police soon found Mr. Welch, with his tools, huddling in the bushes.

Mr. Welch was convicted and sentenced to 143 years in prison. Having succeeded once in escaping, he tried again, and succeeded. In 1985, he absconded out the window of an Illinois prison, lowered himself down a 75-foot electrical cable, and made it all the way to Pittsburgh, where he was arrested again after he illegally parked a stolen car.

“The public will put up with the fact that we don’t successfully rehabilitate people,” Mr. Horn said. “They will not put up with escapes.”