Good Thing I'm Not Studying Crim Law This Semester

Plot summary of the L&O SVU episode I just watched:

• police go to woman's apartment to arrest her daughter.
  
• mother says "you can't arrest her - I did it!"
• police arrest mother; skip to trial - mother pleads not guilty.
• during trial, while testifying, daughter says "you can't convict her - I did it!"
• DA dismisses the case.
  
• someone immediately finds a videotape giving daughter an alibi, proving daughter didn't do it.
• mother can't be retried - double jeopardy.
• mother and daughter live happily ever after.
• (and it turns out that the mother was the one who really did it.)
  

Huh? What? So if I'm on trial for murder, all I have to do is find a friend with an alibi to come testify at my trial and to blurt out "i confess! it was me!" and then we all get to go home and nobody gets charged with perjury or conspiracy or being an accessory or anything? Neat - I'll have to make a note of that - might come in handy some day.