The 'Burbs

On Mayfield Place, a cul-de-sac in the fictional suburban town of Hinkley Hills, Ray Peterson is trying to learn more about his mysterious new next-door neighbors, the Klopeks. Art Weingartner, the Petersons' other next-door neighbor, believes the Klopeks are murderers.
Ray, Art, and veteran Lt. Mark Rumsfield watch Hans Klopek drive his car from the garage to the curb, then carry a large garbage bag from the trunk to the garbage can and bang it with a hoe. During the night, Ray watches the Klopeks digging in their back yard with pick-axes in a rainstorm. The following morning, Art checks the contents of the garbage truck as it is collecting the Klopeks' can. He is joined by Rumsfield and Ray, but they find no human remains.
Bonnie Rumsfield finds neighbor Walter Seznick's dog running loose and wonders if Walter went away. Ray, Art, Bonnie and Ricky Butler go to Walter's house, finding his toupee in the kitchen. Ray collects the dog and leaves a note for Walter explaining the situation. The following night, Ray and Art have a meeting in the Petersons' basement and theorize about Walter's disappearance.
Carol, Ray's wife, grows tired of her friends snooping around the Klopeks' home and she requests that she, Ray, and the Rumsfields pay the Klopeks a visit, meeting Hans, Reuben, and Werner while Art peeks around in the backyard. Later that evening, Ray reveals to Art and Rumsfield that he found Walter's toupee in the Klopeks' basement, which he previously slipped through Walter's mailslot. Ray and the others are convinced the Klopeks have murdered Walter, and the trio agree to investigate the Klopeks' backyard when the owners leave in the morning.
The next day, Carol and son Dave go to visit Carol's sister, leaving Ray to explore the Klopeks' place. After Art disables the Klopeks' security system, he and Ray enter the yard and begin digging while Rumsfield stands guard on his roof. After hours of digging and finding nothing, Ray and Art enter the house, where they discover what they believe to be a crematorium. Ray then begins to dig into the loose soil that constitutes the basement floor, believing there may be bodies buried there.
That evening, the Klopeks come back, only to drive back out when they see lights on in their basement. Rumsfield, Art, and Ricky are shocked to see Walter return home. When the Klopeks return with the police, Art goes into the Klopeks' home to rescue Ray, who hits a gas line with his pick-axe. He yells for Art to flee right before the house explodes into flames with Ray still inside. Ray emerges from the flames just as his wife returns.
Art talks to an officer, who explains that Walter had a medical problem and his family took him to the hospital. While away, Walter had made arrangements for the Klopeks to pick up his mail. When Ray had slipped the toupee through the mail slot, it got picked up with the mail. Ray snaps at Art and declares that the neighbors were wrong about the Klopeks, before lunging at Art and then throwing himself into an ambulance on a gurney.
Joining Ray in the ambulance, Werner Klopek, thinking Ray must have seen the skull of one of his former neighbors in the basement, attempts to murder Ray to collect his skull, revealing that Art was right. Hans assumes the role of the ambulance driver, but crashes into the Weingartners' house during the three-way struggle. The gurney, with Ray and Werner aboard, rolls out of the ambulance and down the street. Ray makes a citizen's arrest on his would-be murderer as Ricky uncovers a large selection of human bones in the Klopeks' trunk. The Klopeks are arrested and the charges against Ray are dropped. Ray tells Ricky that he and his family are going away for a while and that he needs him to keep an eye on the neighborhood.

Question: Who was in the ambulance?
Answer: Ray