KAISERSLAUTERN, Germany — A military judge sentenced an Air Force staff sergeant to three years in a military jail on Thursday for attempting to lure a 13-year-old babysitter into having sex with him and posing for nude photographs.

Staff Sgt. Brian D. Bishop also received a bad conduct discharge, will forfeit all pay and has been reduced to the lowest pay grade, said Erin Zagursky, a spokeswoman at Ramstein Air Base. Bishop, an assistant chief of weather flight operations with the Ramstein-based 86th Operations Support Squadron, pleaded guilty to the charges at a court-martial on Wednesday.

He admitted that he e-mailed the daughter of a U.S. servicemember last August and asked her if she would be willing to pose for money. The girl put her e-mail address on fliers in hopes of landing a babysitting job, and Bishop had obtained the girl’s e-mail from a co-worker who had seen the flier.

The girl’s mother saw the e-mail and notified special agents with the Office of Special Investigations. They used the girl’s e-mail account to pose as the girl and correspond with Bishop.

After several weeks, special agents set up a sting operation. Bishop set up a meeting, thinking he was e-mailing the girl. However, special agents and German law enforcement authorities were waiting for him at an abandoned apartment on base and arrested him.

Bishop had faced a maximum prison sentence of 22 years.