Note: In conjunction with the launch of HuffPost's Crime vertical, senior writer and criminal justice reporter Radley Balko looks at several myths and misconceptions about the criminal justice system. In this first of three installments, Balko looks at double jeopardy, enhanced sentencing and ignorance of the law.

Myth 1: You Can't Be Tried More Than Once For The Same Crime

The Fifth Amendment to the U.S. Constitution states that no person shall "be subject for the same offense to be twice put in jeopardy of life or limb." This protection against "double jeopardy" is intended to prevent the government from retrying the same defendant over and over until prosecutors can get a conviction.

But there are some exceptions. First, the protection only comes into play once a jury has convicted or acquitted a defendant. So in trials that end with a hung jury or a mistrial, the prosecution can usually bring the same charges again. One particularly egregious example is Curtis Flowers of Mississippi, who has been tried an incredible six times for the murder of four people in 1996.

Second, the U.S. Supreme Court has ruled that the government can charge a defendant with both a crime and the conspiracy to commit that crime without violating the constitutional prohibition on double jeopardy. This gives the government two opportunities to convict for essentially the same offense. Conspiracy is often easier to prove than the underlying crime. It also gives prosecutors a way to rope in alleged offenses they can no longer charge separately due to statutes of limitations.

Finally, there is the "separate sovereigns" exception to double jeopardy. This allows a defendant to be tried, convicted and sentenced for the same crime in both state and federal court. The most well-known example of the separate sovereigns exception is when the Los Angeles police officers who beat Rodney King were acquitted in state court, then convicted in federal court of violating King's civil rights.

But it's becoming more common in high-profile cases, where both state and federal prosecutors want a chance at a career-making conviction. Michael Vick, for example, was twice convicted on charges related to his dogfighting operation, once under Virginia law and once under federal law. (He was also indicted on various dogfighting-related crimes and conspiracy to commit those crimes.) As the federal criminal code continues to grow, it seems likely we'll see more examples of defendants who are tried twice for the same crime, particularly in cases involving celebrities and politicians.

Myth 2: The Government Can't Punish You For A Crime Without First Convicting You

Under federal sentencing law, once a defendant has been convicted of any federal crime, when determining a sentence, the judge can consider other crimes he or she may have committed. That includes crimes for which the defendant has never been charged and even crimes for which he or she has been acquitted.

In 2007 Antwuan Ball of Washington, D.C., was charged and tried for a long list of alleged federal crimes, including drug dealing, conspiracy, racketeering and murder. The jury was apparently unimpressed with the prosecution's case. They acquitted Ball on all charges, save for a relatively minor $600 sale of half an ounce of crack. But last March, a federal judge sentenced Ball to 18 years in prison, a disproportionately long sentence the judge said was due to his disagreement with the jury's decision to acquit on the other charges.

According to Douglas Berman, who teaches at the Ohio State University Moritz College of Law and writes the blog Sentencing Law and Policy, three federal appeals courts (the 7th, 8th, and 11th circuits) have allowed judges to consider uncharged or acquitted murders in handing down enhanced sentences to defendants who have been convicted of less serious crimes. In one case, a Virginia defendant was given a life sentence for drugs and firearms charges because the judge found convincing evidence the defendant had been involved in three murders, despite the fact that he had never been charged for those murders, much less convicted.

The doctrine of civil asset forfeiture allows the government to seize the property of people it believes are engaged in criminal conduct before they've been convicted. In fact, the government isn't even required to file criminal charges, only to show some vague connection to criminal activity. Though the policy varies from state to state, the general idea is that the government can seize property if it can show any link between the property and some sort of a crime. The policy is most often used in drug crimes.

Under most civil asset forfeiture laws, the property itself is accused of the crime. The government then files a complaint against the property in civil court. Because it's a civil proceeding, the government's standard of proof is much lower. In fact, in some states the burden is on the property owner to prove he or she earned the property legally. That can be a difficult thing to prove.

The cost of fighting a seizure in court can often exceed the value of the property itself. As of 2008, the federal asset forfeiture fund had over $3 billion in assets. Less than 20 percent of the people from whom that property was taken were ever charged with a crime.

Myth 3: Ignorance Of The Law Is No Defense

Every introductory criminal justice class teaches this one. If you're pulled over for speeding, you can't claim you didn't know the speed limit. If you're pulled over while driving through, for example, in Virginia and the cop notices your radar detector, you can't claim you had no idea the device is illegal in that state.

This particular "myth" is mostly true. And the problem is that it's becoming nearly impossible to know what the law actually is. The U.S. Constitution outlines just three federal crimes -- treason, counterfeiting, and piracy. Various projects have tried to count the number of federal criminal laws passed since, and many have simply given up. But by most estimates, there are at least 4,000 separate criminal laws at the federal level, with another 10,000 to 300,000 regulations that can be enforced criminally.

In his most recent book, the civil libertarian and defense attorney Harvey Silverglate argues that most Americans now unknowingly commit about three felonies per day.

To make matters worse, vaguely-written, broadly-interpreted laws like conspiracy and money laundering give prosecutors yet more discretion and leeway, and make it more difficult for well-intentioned citizens to simply comply with the law. Even the members of Congress who actually pass these laws often don't know what they've just passed, even laws that directly apply to them.

But there is one exception to this rule: If you work for the government, particularly in law enforcement, you can be forgiven for not knowing the law.

Last year, Maryland motorcyclist Anthony Graber was stopped by a state trooper for speeding and reckless driving. The confrontational stop was recorded by Graber's helmet camera, and Graber later posted the audio and video to YouTube. Graber was later raided, arrested, jailed and charged with two felonies for recording his conversation with the state trooper.

Had Graber lived in Illinois, he would have broken the law, and he would be looking at up to 15 years in prison. Several people in Illinois are facing similar charges, and none of them will be permitted to defend themselves by saying they didn't know what they were doing was illegal.

But it turns out that is perfectly legal to record on-duty police officers in Maryland. A state judge later dismissed the charges against Graber in a strongly-worded opinion, stating in no uncertain terms that the cops who raided Graber's home and the prosecutor who charged him were wrong about the law.

But despite the fact that these law enforcement officials wrongly raided, arrested, jailed and charged Graber based on a mistaken understanding of the law, they face no repercussions. It's unlikely Graber will even be able to sue. Prosecutors have absolute immunity from lawsuits related to the decisions they make about whether or not to charge someone with a crime, even when they are clearly wrong about the law.

In a Supreme Court case decided earlier this year, former New Orleans DA Harry Connick and his assistants failed to turn over exculpatory evidence in the case of John Thompson. Thompson was later exonerated of murder, but only after serving 18 years in prison, 14 of them on death row.

In depositions, Connick and his assistants claimed they didn't know the Brady rule, which requires prosecutors to turn over all such evidence. Connick was already protected by absolute immunity, and the Court added that the parish that employed him couldn't be sued either.

A number of studies have shown that while Brady violations are common, they rarely go punished, even in egregious cases that lead to wrongful convictions.

Police officers and most other government employees don't enjoy the broad absolute immunity afforded to prosecutors and judges, but they do have what's known as "qualified immunity:" In order for an officer to be held civilly liable for violating a citizen's rights, the law must be so clearly established that a reasonable person would have known that the officer's actions were illegal.

In Pennsylvania, the courts have repeatedly ruled that it is legal for citizens to record on-duty police officers. But people continue to get arrested for doing so. And so far, federal courts have refused to allow those who have been arrested to sue the law enforcement officials who arrested them, even though the officials did so illegally.

Last February, police officers in Philadelphia confronted Mark Fiorino for openly carrying a handgun in the city. They then threw Fiorino to the ground, handcuffed him, pointed their guns at him, and repeatedly threatened to kill him.

As it turns out, Fiorino had done nothing illegal. He had his gun permit with him, a fact he told the officers when they tried to arrest him. The police officers didn't know the gun laws in their own city. Fiorino did.

Not only were the officers not punished for nearly killing a man who had done nothing wrong, Philadelphia District Attorney R. Seth Williams then charged Fiorino with reckless endangerment and disorderly conduct because Fiorino had a tape recorder with him, and recorded the entire confrontation.

CORRECTION: An earlier version of this story stated that Mark Fiorino was jailed after his altercation with police in Philadelphia. Though he was later charged and tried for a felony, Fiorino was released at the scene and wasn't jailed.

Coming Wednesday: Looking at misconceptions about appeals courts, holding public officials to a higher standard and "getting off on a technicality."