In one episode, Howard laces a beverage for Sheldon with tranquilizers. In another, he admits to administering sleeping pills to his mother without her knowledge. What is that IRL, assault?
Most of the group have committed criminal acts…
Penny, Sheldon, Howard, Raj, and Leonard assaulted the guy that stole Sheldon’s WoW account. Penny was the one that kicked the guy in the balls, but the others were accessories before, during, and after the fact.
Sheldon stole the Raiders of the Lost Ark film from the theater when they didn’t get tickets.
Howard, in addition to his acts in the OP, drove a Mars rover into a ravine to impress a girl, then he and Sheldon and maybe Raj wiped the computer records.
Leonard probably divulged classified information to a North Korean agent, and it was his rocket fuel that exploded to kill the elevator.
Bernadette, Penny, and Amy stole clothing from a charity drop box thingy.
Amy hit Penny while trying to hit Bernadette.
Bernadette keyed Amy’s car.
Howard drugged Sheldon’s milk and returned him to the apartment.
Sheldon has hacked multiple government computer systems.
I don’t think Stuart has been shown to commit any crime–but he may have burned down his store.
Bernadette is pretty lax in her handling of biohazards, which would get the interest of both OSHA and California state regulators.
Sheldon has broken into Penny’s apartment several times.
Howard “borrowed” a robotic arm.
If they ever have a final episode maybe they will all go to jail? Oh wait, wasn’t that done already somewhere?
Yes, but look at it from Howard’s point of view - she was a girl!
Yes, but look at it from Leonard’s point of view - not only was she a girl, but she was both hot and willing to make out with him. 
I’ve never seen this show, but you folks are making it sound like a spinoff of Oz.
Howard also had sex with his cousin. Depending on the jurisdiction that could make him a sex offender.
Howard said she was his second cousin, IIRC. Plus, marriage restrictions aside, where in the US is just sex with a cousin illegal?
Leonard probably divulged that he was working on a rocket fuel to the N Korean girl. I don’t think he got as far as revealing any details. Still, it was poor judgement.
Well Howard is a known associate of Eddie Krispo.
She was only down to her underwear when Sheldon interrupted them, so he probably hadn’t told her the formula. Which is unfortunate, because if the Norks used it unchanged, it would have devastated their rocket program. 
or at least blown up all of their elevators…
In The Panty Piñata Polarization, Howard “borrows” a NORAD drone to try and find the house with the models in it. Later, Howard and Raj lie to enter the house (and who knows what other bad things they did after they entered it).
In* The Flaming Spittoon Acquisition*, Sheldon has someone gotten in Amy’s apartment without her permission while she was on a date with Stuart.
In The Wildebeest Implementation, Penny buys some shoes intending to return them after wearing them a bit. (But I don’t think she follows thru.) An iffy plan, IMHO.
It is revealed in The Electric Can Opener Fluctuation that Leonard, Raj and Howard tricked Sheldon into thinking he made a major discovery (using an electric can opener, of course). Since their research was supported by the NSF, this would constitute fraud and waste of US government resources.
How can I forget Howard and his spy cameras.
In The Cooper-Hofstadter Polarization, Howard is using a remote control model car with a camera to peek up Penny’s skirt. The legal status of laws against such practices is currently up in the air.
In The Bad Fish Paradigm, Howard (and Raj) have mounted a camera near the elevator and are spying on Leonard and Penny after their first real date. While the two are in public, mounting a camera without the landlord’s permission is presumably illegal.
In The Hot Troll Deviation it’s revealed that Howard gave Penny a stuffed bear with a webcam hidden inside. Definitely illegal.
Note that hiring prostitutes is illegal in California and Las Vegas. Howard apparently several times in the former, Raj and Leonard (on behalf of Howard) in the latter.
The three only were fooling Sheldon, they weren’t going to publish the wrong results.
Nonetheless, they interfered with the real research. Time and effort were wasted and perhaps something important was missed while the can opener was fluctuating. Leonard claimed the real data was saved, but I doubt this was possible.
Also in The Speckerman Recurrence (the same one where the women robbed a charity box), Penny relates a bullying incidence she participated in that was definitely grounds for a good length prison sentence.
In The Tangerine Factor, Raj has found a busted iPod outside L&S’s building. He says he’s going to sell it on eBay as “slightly used”. That’s fraud right there.
Note that this can’t be the same iPod Penny threw out the window earlier as they are different colors! But still that’s damaging someone else’s property by Penny.
Leonard was driving at 120 mph coming home from Big Sur Spa and Resort in “The Love Car Displacement.”
I do not think the error was in the formula for the fuel, but just in Leonard’s calculations of the proportions when he mixed up a sample batch to bring home to the apartment. But I agree that he never got so far as to actually reveal any secrets to Joyce Kim.
But, while we are on crimes they did commit, didn’t Raj (I think, or possibly Howard himself) commandeer a NASA satellite to photograph Howard’s wedding from space?
Sheldon has, I think, violated more than one restraining order taken out against him by various of his heroes.
Didn’t Stuart offer Penny some of his drugs/medication?
I thought I remembered a scene with him plopping a bunch of prescription meds on the counter of his store. I thought the implication was she could have some, but I don’t remember.
Pretty sure they just timed it to coincide with when Google was passing overhead to take pictures for Google Map (which I imagine might be a NASA satellite, but I don’t think they rerouted it - just took advantage of knowledge of when it would be photographing their building).