Saved by the Bell: Wedding in Las Vegas

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Zack returns home and discovers that his father disapproves of Zack's upcoming wedding to Kelly, and thus will not fund the ceremony. Zack decides to pull off some kind of wedding with the $1,200 he has. Melanie gives Zack two free passes to stay at the Stardust Hotel in Las Vegas.
The next day, Kelly, Slater, Screech and Lisa arrive at Zack's house and begin packing their cars for the trip to Las Vegas. Zack makes a bet with Lisa that the guys will make it there first. The girls accept the bet and that's when the troubles begin.
As they race down a back road, the guys are pulled over by a local sheriff. The sheriff arrests them under suspicion of theft.
Meanwhile, on another back road, the girls burn out their radiator. Finally, a man by the name of Kurt Martin appears walking down the road. He tells them that he was on his way to Las Vegas. He fixes the fan belt by using Lisa's expensive belt and replenishes the radiator with the girls drinking water. In return, he asks to be driven to Las Vegas. The girls get to Las Vegas first.
Meanwhile, the boys get booked, photographed and thrown into a jail cell with a yuppy murderer, named Herb, and a biker/poet, named Ray. Finally the sheriff decides that the guys aren't suspects when he learns that the stolen Bronco was found and the real culprits were arrested in San Diego. But the Sheriff extorts $1,200 from Zack to let them out of the jail.
In Las Vegas, the girls admire the $4 million Considine Diamond on display in the Stardust lobby. That evening, the guys finally arrive at the Stardust, and Slater eyes a pretty girl in the lobby. Lisa and Kelly see the rest of the guys and they are reunited.
The next morning, the guys attempt to get work as caddies at a golf course. Here Slater once again runs into the pretty girl, whose name is Carla, and she works as a cashier at the pro shop. The guys get fired and earn no money.
The guys and girls play around in the hotel pool. Here, Slater again runs into Carla who agrees to go out with him. Meanwhile at the hotel's restaurant, Zack and Screech run into Bert Banner; who overhears their money problem and offers them jobs as male escorts.
The next morning, Bert trains Zack and Screech as escorts at his office, making Zack late for a meeting with a wedding coordinator which angers Kelly.
That evening, Screech gets his escort assignment: a heavyset, southern woman named Diana that rides around in a pink limousine. Diana picks Screech up and takes him to a formal dance club where she dances the tango with him.
Meanwhile, Zack is forced to dine with Kelly at the Top of the Strip Restaurant at the Union Plaza Hotel while he dines at the same time with his escort: a Russian woman named Katrina. But Kelly soon figures out what's going on. After Kelly follows Zack to Katrina's table, she tells him that the wedding is off and storms out. After Zack leaves the restaurant depressed, Slater arrives at the same restaurant with Carla.
Zack goes to Kelly's room at the Stardust, but she and Lisa won't let him in. Zack goes into his room next door and climbs out onto the balcony to climb over the railing to get to Kelly's balcony to talk to her.
Back at the restaurant, Slater's date is interrupted when Carla's ex-boyfriend Freddy Silver, a mobster, arrives and yells at her for going behind his back in seeing someone else. When Slater knocks Freddy down, he and Carla are forced to run when the two thugs appear, who turn out to be Freddy's bodyguards. Slater and Carla run back to their room at the Stardust. But when they go out onto the balcony, they surprise Zack who slips and almost falls.
In the girls room, Zack explains everything to Kelly and she forgives him. Next, Carla tells the gang that Freddy wants her and all of them dead because she knows that he's in town to steal the Considine Diamond.
Lisa gets Kurt to help smuggle Slater and Carla out of the hotel by putting them in a luggage rack. But when they get to the hotel's main entrance, Screech, returning from his escort assignment, knocks over the luggage rack, exposing Slater and Carla. So Zack grabs Screech and the four of them get into Slater's Bronco. Freddy's thugs commandeer a taxi and take off after them, followed by Kelly, Lisa and Kurt in Lisa's BMW.
A car chase ensues. Zack, Slater, Screech and Carla abandon their Bronco in a traffic jam at the end of Fremont Street and escape by hiding out in a wax museum by impersonating waxwork figures. But on the street, the four are spotted again by Freddy's thugs who chase them into a casino. The guys and Carla sneak into a Las Vegas dance show dressed as showgirls. But backstage, they're all captured by the thugs as well as Lisa, Kelly and Kurt who stumble by.
The gang is taken to Freddy's room where they fail to talk their way to freedom. But Kurt suddenly announces that he is the son of the Stardust Hotel owner and he tells Freddy that he can get him to the diamond. Freddy still refuses to let any of them go and he forces Kurt to take them to the vault where the diamond is. Kurt opens the vault, and when Freddy and one of his thugs go in, Zack, Slater and Screech once again pull off their "Three Stooges" routine and trick the thug guarding them. They push him into the vault and the gang locks Freddy and his two thugs in it.
After everything is resolved, the gang immediately goes to the nearest wedding chapel for Kelly and Zack to get married. The Silver Bells Chapel is run by Bert Banner! Just as he is about to marry them, Derek and Melanie Morris burst in. They tell them that Slater had earlier called them and convinced them to respect Zack and Kelly for what they are doing, so they have a change of heart: they now support Zack and Kelly's marriage.
A few days later, there is a wedding held in a park near the Stardust Hotel, with Lisa being the Maid of Honor and Screech being Zack's best man along with Slater. The wedding march begins and Kelly is escorted down the aisle by her father, Frank Kapowski. As the ceremony begins, Jessie Spano suddenly bursts in saying that she couldn't miss the wedding for the world, making the gang of Bayside complete. A montage shows Zack and Kelly's up's and downs from "Saved By the Bell" from 9th grade to the college years. Zack and Kelly recite their vows, the minister pronounces them man and wife. After the ceremony, Zack and Kelly are congratulated one by one by the gang as well as Mike Rogers, Alex Tabor and even Richard Belding. Kelly gets a tearful congrats from Jessie. Slater gives a toast to all assembled who include Kurt and Carla. Kelly's parents Frank and Carol, congratulate her and Melanie and Derek congratulate Zack.
That evening, Lisa and Kurt (now a couple) say goodbye to Zack and Kelly who are packing their stuff into a limo to take them on their honeymoon. Screech gives them a tearful goodbye as do Slater and Carla (also a couple). Slater says: "It's the end of an era." Kelly throws the bouquet to Screech who catches it. Then Diana suddenly appears and chases Screech away. Zack and Kelly then take off in the limo as the screen fades to the credits.

Question: Why are they arrested?
Answer: Suspicion of theft