Lupe Ramos, who works nearby one of the sites that had been targeted, came to work last week to find a mess of empty bottles, broken windows and balloons, which police say are used to hold nitrous oxide.
Officers had arrested 40 people, nearly half of them juveniles, at the warehouse party last Saturday night. They say such break-ins have become more common with the slow economy leaving buildings vacant for much longer.
"They break in through roll-up doors, through windows, have the parties and they go undetected until we get calls," said Santa Ana Police Corp. Anthony Bertagna.
Police said the illegal raves are well-planned, with promoters getting the word out through social networking sites.
Police said that other illegal parties have involved shootings and stabbings.
Lupe Ramos now avoids late night trips to her business. "It's terrible. I think twice before coming here because you never know what you're going to find."
Police advise owners of empty buildings to secure the spaces more carefully and watch for signs of "scouts" that case empty buildings before planning an illegal party there.
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