Hostage, a person held in captivity to assure that an agreement is observed or to coerce another party into taking (or not taking) some action. Countries in ancient and medieval times sometimes exchanged hostages, often persons of high rank, who could be put to death if certain agreements were broken. Invading armies often take hostages of local citizens to discourage resistance to their occupation. Terrorists sometimes seize hostages both to force concessions from governments and to gain publicity for their cause.
What if your pen pal was a prison inmate? That's the idea behind a prison project designed to connect middle school students with prisoners. What influence did these pen pals have on kids?
State troopers are associated with highway patrol, but their duties extend past the asphalt. They are involved in everything from highway enforcement to criminal investigations. What else are state troopers involved in?