Criminal Justice is a HUGE field consisting of many more opportunities than just patrol style police.  Let's use Chester the Molester for an example.

The Police

Chester got arrested by a police officer.  This department is likely made up of patrol, investigations, traffic enforcement, administrative staff, the executives (IE Chief, Asst. Chief, etc.).

The Jail

Chester will get booked and cooked by a jail intake officer. If Chester get's silly in jail, he will get beat down, um...I mean "subdued" by a jailer, likely a sheriff's deputy of the respective county.  Sheriff's often also do many if not all of the same roles as the police with the added responsibilities of the jail, probation office, overseeing some court administration and security, serving warrants, etc.

The Court

Chester will go into a court room where there will be a bailiff, transport deputies to make sure he arrives safely, a court clerk or court appointed investigator (sometimes a probation officer but not likely in this case) who will at times appraise the judge of Chester's background, education, societal status, etc. in an effort to determine an appropriate bail, which will not be granted in this case.  The judge will have various clerks and administrative staff who will ensure that every "I" is dotted and "T" is crossed in order to guarantee Chester gets a fair trial.

Corrections

Once Chester is convicted he will be sent to a prison.  In some states prisons are private, in others they are state employees and still in others they are Federal employees.  Corrections Officers have a tough job, but a necessary one.  These are the people who ensure that Chester doesn't get out to hurt anyone else.  One thing to note is that frequently in corrections the turnover rate is high, due to of course the tough nature of the job.  But some people love it and with a degree you can move up very rapidly.  Corrections also have various roles of investigators, teachers, psychologists, medical staff, administrative staff, executive staff (Warden, Asst. Warden) preachers, counselors, Special Response Teams (SRT, SWAT, or SORT), along with patrol (in very large prisons) and of course the old "turn key". 

Parole will review Chester's file to see if he is eligible for early, supervised release.  Not likely.

And that's pretty much it for Chester.

Some other occupations to consider are:

• Private sector: investigator, insurance adjuster or investigator, auditor, security, loss prevention, risk mitigation, etc.  There are a lot of private opportunities, many pay much more than law enforcement. 
  

• State law enforcement.  Everything from investigations to highway patrol.  Of course in Texas we have the Texas Rangers (not the crappy baseball team).
  
  
• Constables (usually court "go-fors").  You know, the guys who serve subpoenas, misdemeanor warrants, perform some investigations, prepare some documents, sometimes patrol, sometimes they also transport prisoners and evict people, enforce court orders etc.  Think of them as the "judge's police" and you get the idea.
  
  
• The Marshall's Office. Much like a constable but often they serve like a hybrid of the police, constable's office and sheriff.
  
  
• Federal Law Enforcement.  All of the alphabet agencies here, the FBI (though you'd do better majoring in Accounting than Criminal Justice with them) the DEA, the DHS, the ATF, the DOJ, the Border Patrol, the Secret Service, Capital Police, etc.  These positions are so diverse, of specific jurisdiction and have so many different types of jobs it would take a book to cover them all.  Generally they fall into three categories in the following:

• 1.) Investigations = this is the bread and butter of most FLE.
• 2.) Protective services = everything from gate guards to the President's own escort.
• 3.) Patrol and police services = think of the Park Services, Border Patrol, etc.
  

Lastly there is the military, which is its own thing altogether and I don't have any experience here to speak of, but I do know that they have Military Police, investigators, etc.

I'm sure I've forgotten somebody ... but there you have most of it anyways.

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