"If anything bad happened, if the kids violated the rules, they'd be sent home," Gansler said. "My guess is ... that if someone drank beer, that would not be an offense for which the chaperones would want to send somebody home."
Delaware law, like Maryland's, does not distinguish among types of alcohol in its broad prohibition against underage drinking. In both states, the legal drinking age is 21.
It is legal for parents to allow their own children to drink at home.
In several photos posted online by people at the party, older adults can be seen standing in the background. In videos and photos, young people, both men and women, are dancing on a bar and on a table. In one video, a bucket of clear liquid is poured from the balcony onto dancers below. It's unclear how many teens were drinking.
Some of the videos have since been removed from social media.
"I don't remember much, but it was one of the best parties I've been to, hands down," said one attendee who spoke to The Baltimore Sun this week under the condition of anonymity because some engaged in underage drinking.
Two days after the party, however, the house was in bad shape. Julie Barnes, who has for years cleaned the home after renters, said she arrived on June 15 to find the wooden floors rippled from moisture damage, dents that appeared to be made from high heels on the bar and pool table, and floors sticky from what smelled like beer. According to minutes of a South Bethany Town Council meeting where the vandalism was discussed, the house sustained about $50,000 worth of damage.
Police who investigated did not place blame on the Landon group and classified the damage as likely the result of a burglary that occurred sometime between Friday evening and Saturday when Barnes arrived to clean. The Landon group turned in their keys Friday afternoon, parents said.
A parent who chaperoned the night of the party but would not discuss whether there was drinking said he helped the boys clean up the next morning. He said they left the house in good shape. Another parent said a representative of the realty company ResortQuest called afterward to say the house was fine and minor damage would be covered by the security deposit. The parents asked not to be identified to protect their children's privacy. Representatives from ResortQuest did not respond to a request for comment.
Gansler said the parents assume that someone broke in and trashed the house after the boys checked out.
"Apparently, the night before, the parents who were chaperoning it kicked kids out" because it was getting too crowded, Gansler said. "The thought was [the damage] was so malicious that they were trying to get revenge or back at the parents who were chaperoning for kicking them out."
The home's owner, Timothy Dickson, lives in Virginia and said he thought he and his wife were renting to several families vacationing together, not to a dozen recent high school graduates. He said they were dismayed by the teens' behavior at their beach house as displayed on social media.
Baltimore Sun community coordinator Michael Gold contributed to this article.