Probable Cause is a set of facts and circumstances that would lead a reasonable person to believe that a violation of the law has been committed.

A peace officer gets a little more latitude, however, because if they have "experience and training" to the matter at hand, the courts recognize that they might notice something that an ordinary citizen might not.

Good examples of PC are offenses committed in the officer's presence or view, like public intoxication or fighting in public (garden variety breaches of the peace, contraband in plain view, like stolen property or a weapon, the odors associated with a criminal act, such as the smell of marihuana or the odor of alcohol on a drivers breath and anything else that would be immediately recoginzable as proof to a "reasonable person" that a crime had been committed.

Hope that clears things up a little. If you have specific questions about PC in different situations, ask away.

Go to the police academy or law school, if you really want an answer to that question.  It's just not a simple issue.  Judges and lawyers are forever arguing and making new caselaw about what probable cause really is.  I'm not trying to be a smartass, the issue is just a lot more complicated than many folks seem to realize.

If you want the technical definition, it is that the LEO, under the totality of the circumstances then present, has reasonable cause to believe that it is more likely than not that contraband or evidence of a crime is located in the area in question.  Now, the officer is allowed to take into consideration his or her training and previous experience when interpreting the facts at hand.  "Hunches" don't count, you have to be able to articulate to the court specific reasons why you felt you had PC.  For instance, I stop a car for speeding.  It's one in the morning in an area known for drug trafficking.  I walk up to the car, the driver hurriedly gets out to meet me.  He is nervous and sweating, even though it's 50 degrees outside.  For my safety, I ask him to get back in the car (yes, I can order him back into the car even if all I have is a traffic infraction- the U.S. Supreme Court ruled a while ago that officers have the right to control drivers and passengers on normal traffic stops for safety reasons.  I do not have to be able to articulate specific reasons why I thought this particular person was a threat, I can tell them to do basic things like get back into or get out of the car simply for my safety).  I walk up to the car behind him, see him stuff something under the seat.  I look in the window and see some small rubber balloons lying on the floorboard, tightly tied with small pieces of some substance inside.  Since I've worked dope, I know based on my training and experience that drug dealers frequently package drugs, especially heroin, in such balloons.  Because I have that training and experience, I now have PC to search the car.  An officer who doesn't have the same training and experience and cannot articulate the drug packaging may not have PC at this point, even though they are suspicious.  However, his nervousness and his stuffing something under the seat definitely give me reasonable suspicion to do a 'pat-down' search of the area under the seat for a weapon.  In fact, as soon as he reaches under the seat he's probably going to get a gun screwed in his ear.

The problem lies not in the technical definition of probable cause, but in the fact that PC is something that the officer has to decide he or she has based on the totality of the circumstances.  Every situation is different, and every officer has slightly different training and experience.  That decision about having PC will then be second-guessed by attorneys and judges who have the benefit of evaluating the situation after the fact and having all the information.  It's impossible to make one concrete, hard and fast rule that can quickly and easily be applied in every situation that an officer could possibly face.  If you think you're frustrated with PC or search and seizure law, try working the streets for a few years.  Just when you've got it somewhat licked, the courts come out with a new ruling that changes everything.

with the new terrorism laws, the government can do what they want, when they want, to any person or group that they want.  

our bureaucratic royalty has just voted our freedom and the BOR away until 2005.  odds of getting the rights back are about the same as the repeal of the AW and hi-cap bans.

You may be right as far as the federal government goes, but that anti-terrorism bill isn't going to change how the state and local LEO's do business.  The only time it will affect us is on large cases that we end up working with the feds on, and those really aren't that common.  Remember that 'The Government' is not one single huge entity- you've got city agencies, county agencies, state agencies, and then all the myriad branches of federal law enforcement who all have different missions, different ways of doing things, and really don't like each other or work well together, in many cases.

PC is a dirty cop's wet dream. Do an illegal search, then make up some crap later about "specialized training" or "previous experience".

Gun stuffed way under the seat? No, the butt was sticking out. Musta happened when the guy hit the brakes too hard one time.

Some dope buried deep in a pocket? No, I saw the baggie sticking out of his pocket, and I know from my "specialized training" or "previous experience" that dope is carried in baggies.

Sweating? Nervous? Too much eye contact? Not enough eye conact? Too calm? Too much movement in the car? All things that will hold up in court when it's the officer versus the perp.

You may have pulled the guy over for being the wrong color for the neighborhood (DWB-Driving While Black) but don't EVER admit it on the stand in court. "His tail light was not working". Nevermind that it was working in the impound lot. "Must have been a loose connection".

Not to take away from the good cops out there, but dirty cops know how to get the job done.

All the replies above are right on target but maybe I can contribute just a bit.  It was explained to us in the academy, it's like a set of building blocks.  PC is not anything set in stone.  It pieces of a puzzle that you have to put together.

The building block thing is something like this.  Start at the bottom and work your way up.  You got to have all the steps to articulate PC.  If you don't have a step, then it can be squashed in court.


           Probable Cause  
           ^^^^^^^^^^^^^^
             
Facts:  A smell, blood
       paraphernailia,

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                      
Reasonable Sus:  Evidence Pointing towards:
                acting strange, nervous behav.
           
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Suspicion:  A belief something is
          taking place or a miss


Starting at the bottom and working your way up, but there are times when you have your PC, w/o having to work your way up.  Such as:  a 911 hangup, go to residence, open door, man standing over women who is bleeding profusely, knife in hand.  This would be probable cause that a crime has taken place.  Find some case law on this stuff.  It will help to understand, it's a difficult area to work and it can get you in trouble because, if you are not able to articulate your PC for your actions, then everything found is considered fruits of the poisonous tree. The evidence can and has been surpressed in court.  No evidence, no coviction, you and your department get sued.

Hope this helps.

(I think my diagram is correct. Sparky and natez did I miss anything?)



Edited because the original diagram didn't post like I wanted it to.

GovtThug, I truly wish I could tell you that you're full of shit, but unfortunately you're not.  I know that stuff goes on, and I've seen it happen.  I've called people on it and tried to drill newbies with the proper way to do things, but unfortunately cops are people, and you're just not going to get perfection.  It's a fine line to walk between doing your job, digging and finding bad guys and crossing the line in order to get another bust.  Too many cops feel that it's okay to bend the rules, 'cause after all, they're getting the drugs and the guns off the street.  Unfortunately, what they don't realize is that they are costing us our credibility with the general public.  People don't think about the thousands of cops who do their jobs honorably every day- they remember the latest news story about the ones who broke the rules and got caught.

As long as policing is done by people, you are going to have some problems.  If anyone has a solution, I'd sure like to hear it.