In order to convict a person of burglary, the prosecutor must prove that the defendant entered a building or structure without permission and with the intent to commit a crime inside. Without proof of intent to commit a crime, a person who unlawfully enters a building or structure can likely be convicted of trespass or some other crime, but not burglary.
Say a person enters a closed concert hall to see a musician rehearse. The person is a huge fan and only wanted to see the musician. Now say the person entered the closed concert hall to harass and throw rocks at the musician (assault). The fan in the first example has committed trespass but not burglary because wanting to see a musician isn't a crime. But the person sneaking in to throw rocks at the musician could be charged with burglary because the person snuck into the concert hall intending to commit the crimes of harassment and assault. The person's intent to commit a crime changes the same unlawful entry (sneaking into the concert hall) from trespass to burglary.
Note that burglary only requires proof of the intent to commit the crime not that a crime occurred. In the concert hall example, say the person gets caught by security with rocks in hand but hasn't thrown them—the person can still be charged with burglary because the intent was there.
Prosecutors have several different ways in which to prove the defendant's criminal intent.
Oftentimes, defendants will confess to police (or others) that they entered a building intending to steal or for some other nefarious purpose. For example, police respond to an alarm and find a teenager inside a home. The teenager blurts out, "I wasn't going to hurt anyone, I was just looking for something to sell." The teen just admitted to entering the building with the intent to commit a crime, theft. A jury would likely find the teenager guilty of burglary.
Other times, the defendant's actions are really consistent only with an intent to steal or commit some other crime. Suppose a man breaks into a woman's house in the middle of the night, and she finds him in her closet rifling through her things. The man and the woman have never met before. Her door was locked and he pried the door open with a screwdriver. Most jurors and judges would have a hard time imagining that defendant had any intention—other than the intent to commit a crime—when he entered the woman's house.
Similarly, the person sneaking into the concert hall who has rocks in hand and is aiming to hurl them at the musician would have a tough time providing a different, plausible explanation for the rocks. But let's assume the security guard found the person sneaking in but the rocks are still in a backpack. Here, the prosecutor might need to use other evidence of intent, such as the backpack also contained a lockpick, threatening notes directed at the musician, and pepper spray.
State law varies on whether prior burglaries can be used to prove a defendant's criminal intent. If the defendant has previously been convicted of burglary, then the prosecutor may, in some states, introduce evidence of the prior burglary to show that defendant had criminal intent during the current burglary as well. The theory behind allowing such evidence to prove intent is that a law-abiding defendant who has been prosecuted and convicted for burglary in the past will be very careful in the future. A person who had already been punished for burglary would know better than to go into a building or structure without permission and would only do so if he or she were up to no good.
For example, suppose a defendant was arrested three years ago for going into a neighbor's garage and stealing tools. Yesterday, the same defendant was arrested after being seen going into a different neighbor's garage. The police find the defendant with some of the neighbor's tools in his truck. At trial, the prosecutor may be able to introduce evidence that the defendant committed a prior similar burglary to show that defendant had the intent to steal tools when he entered the garage.
In other states, evidence of prior burglaries cannot be introduced. Even in states that allow such evidence, courts must carefully tell the jury how to use the evidence. The jury cannot use the evidence to decide that defendant is generally a bad person. The evidence can only be used to decide whether the defendant committed the crime or had the intent to steal. For example, if a defendant argues that he was high on drugs and went into a garage to lay down and sleep off his high, the evidence of a prior garage burglary is relevant to show that defendant entered the garage with the intent to steal. However, if the defendant argues that he was not the person seen going into the garage, the court may be less likely to allow the evidence of the prior conviction because the jury has to determine the identity of the burglar, not the burglar's intent.
Sometimes, evidence of a prior burglary conviction will be admitted only if the prior crime was uniquely similar to the charged offense in the way it was carried out. It will be admitted in order to prove the criminal's identity. For example, suppose an assailant neatly cut a hole in a window above the door, entered and left the glass disc on the kitchen table, and then helped himself to food in the fridge before sneaking upstairs to commit a sexual assault. At trial, the defendant, who was captured a block away from the crime, claims not to be the assailant. A judge might admit evidence that this defendant has a prior burglary and assault conviction that involved the same bizarre behavior, in order to prove that the defendant was the assailant in the current case. Contrast this scenario with that of a defendant who was previously convicted of breaking into a store to commit theft and later arrested for breaking into a home to commit an assault. The two crimes might be too dissimilar to allow the prosecutor to use the prior conviction as evidence.
If you are charged with burglary or any other crime, you should talk to a local criminal defense attorney. An attorney can explain the charges and the criminal process, protect your rights, and work to obtain the best possible outcome.