Creed Bratton is The Office's in-house weirdo. While he isn't much more than background noise in the first season and he's pretty much incoherent in the last season, in the in-between, there is a very clear picture of who Creed Bratton is, and one of the bullet points under his character portrait is criminal. There are plenty of examples of Creed Bratton committing crimes right there on the show, but a lot has to be inferred by what he talks about when he's still making sense, and it doesn't look good for Creed. In the end, it all catches up to him as he is led away by the police, albeit peacefully.
Here's a comprehensive list of the crimes that Creed Bratton either overtly committed on camera or could reasonably be assumed he committed based on his actions.
Theft
The question isn't if Creed Bratton has committed theft, but how many times he has committed theft. The first time we see it for sure is when Michael Scott is forced to commit theft at the Chinese food restaurant where he "dined so much."
When the collage of photos is shown of people who have stolen from the restaurant, one is Creed. Another is Creed in a brown wig. The fact that he has stolen from the same Chinese restaurant twice makes one wonder where else he has stolen from.
Indecent Exposure
To Creed, Indecent Exposure isn't a big deal, it's just "hanging brain." When Phyllis is flashed in the Dunder Mifflin parking lot, the office rises up in support of her. All except Michael and Creed. The latter of whom had this to say: "the guy was just hanging brain. I mean, what's all the fuss? If that's flashing, then lock me up."
Perhaps a foreshadowing of how his character arc would eventually reach its conclusion, but this is another crime that Creed very clearly committed. Fortunately, we didn't have to see it to believe it.
Identity Theft
Obviously. It's right there in the fourth season when Creed admits to once being William Charles Schneider, (more on that later). It comes up again in the fifth season. "Nobody steals from Creed Bratton and gets away with it. The last person to do this disappeared. His name: Creed Bratton."
Meaning that Creed was stolen from then turned right around, made that Creed disappear (more on that later), and then assumed an identity that wasn't his own, which is identity theft in the clearest definition of the crime.
Fraud
When Creed admits to identity theft in season five, he is following up on his previous admission to once being William Charles Schneider, which we learned in season four. However, the identity theft goes even further than that, with Creed saying, "Creed Bratton has never declared bankruptcy. When Creed Bratton gets in trouble, he transfers his debt to William Charles Schneider."
Which translates to Creed using criminal deception towards financial gain. Also known as fraud. Another example is when Creed starts selling off his computer parts, thinking Dunder Mifflin is going out of business. Creed is quite the fraudulent fellow.
Drug Possession
Again, the question isn't if Creed Bratton has ever been caught in possession of drugs, but what drugs he hasn't been caught in possession of. Without all the obvious references to the drugs he's done, both in the 60s and in every single decade since, his behavior is indicative of someone actively partaking.
Not to mention he got heroin from the Taliban. Let's not forget about that. He has definitely been caught in possession at least once, and that rap sheet is probably most populated by drug use and possession.
Kidnapping
Whatever happened to the original Creed Bratton when he stole from the new Creed Bratton, he had to be taken against his will at some point. Even if Creed didn't do that himself and instead paid someone else to do it, he would still be an accomplice to an abduction that lead to the disappearance of another human being.
Thus, it can almost be guaranteed that Creed participated in kidnapping in some way. Turns out that identity theft can get a bit messy. More on that later.
Racketeering and Extortion
Defined as creating a "problem" in order to drive people into forfeiting financial resources—which also earns him a theoretical extortion charge—racketeering is hinted at when Creed talks about his time in cults. He says that it's more fun to be a member of a cult, but there's more money in being the leader of a cult.
Which means it's very possible that Creed is guilty of creating an entire racket by starting his own cult for financial gain. Creative, Creed. Definitely creative.
Evading Arrest
The fact that Creed Bratton is still at work at Dunder Mifflin throughout all of this is a good indication that he has been evading arrest for years, if not decades. But, even if he has served his time for whatever he committed decades back, in the series finale, when he is discovered at Dunder Mifflin, essentially living there, it's clear he is on the run.
This culminates in him finally being arrested and led away by the police. Given how peaceably he goes and how unlikely it is that any of his coworkers turned him in, the assumption is that he called the police on himself and finally turned himself in for all the crimes he committed.
DUI
Not something that we've seen and probably not something the show would actively joke about despite a clear lack of boundaries at times, but still something that you can probably bet on Creed having committed. Being someone that is often, if not always, on some kind of mind-altering substance, as well as someone who has his own car and drives, it stands to reason that, at some point in his drug-fueled escapades, he has been pulled over and charged with a DUI.
Murder
Or, as Dwight's friend Trevor calls it, "the big 'M'." Creed Bratton was obviously never seen committing murder, but there are three major hints that he actually has committed the crime. The first comes when Creed admits to the documentary crew that the last Creed Bratton "disappeared" before the current Creed, our Creed, assumed his identity.
The next comes when Michael Scott is hosting an office-wide game of Belles, Bourbon, and Bullets. Creed arrives late to work, and Michael tells him, "there has been a murder, and you are a suspect." Creed flees the scene. The third comes in another classic Halloween episode. Creed shows up to work with a blood-splattered shirt and tells the camera that it's a very fortunate day to be Halloween. Now, maybe Creed is just a butcher, or maybe he was channeling his inner Jackson Pollock, but it's more likely that he is, in fact, a murderer.