Dallas police are investigating a string of Lake Highlands area burglaries.
Police said the area has had as many as 10 cat burglaries in the last few weeks. Purses, electronics and jewelry have been stolen. Residents left the windows unlocked in all of the cases.
"It's a real hard lesson for us, but we've learned it," victim Kristen Cantrell said.
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Her home near Plano Road and Walnut Hill Lane was hit sometime before 7:15 a.m. on April 12.
"They evidently came in, in the middle of the night, and we were asleep, never woke up," she said. "And the next morning, when I was getting ready to leave, my purse was gone."
Cantrell said her sleeping dog did not wake up, either. She found muddy footprints on her kitchen sink and floor.
Police said this type of burglar likes the thrill of breaking into homes while knowing people are home.
Investigators originally thought one person was responsible for the break-ins but now believe there may be more than one burglar in the neighborhood.
The latest burglary happened early Sunday morning in the Merriman Park Estates neighborhood near Walnut Hill Lane and Skillman Street.
Jewelry and a computer were taken in that burglary, and muddy footprints were found beside the bed where the resident was sleeping.
Merriman Park Estates resident Connie Schaefer heard about the break-in from a crime watch email.
"Everybody has spread the word," she said.
With pleasant evenings lately, it has been good to open windows, Schaefer said.
"When I open one when the weather's nice, I'm so afraid I'll forget to lock it," she said.
Cantrell said she is locking her windows to avoid another break in. But she also said it might have been more dangerous if she had seen the burglar.
"It could have been worse," she said. "I know that I've heard about in the news lately that there've been some stories where there were home invasions and people lost their lives, so I'm angry that I didn't wake up and I'm kind of grateful that I didn't wake up."
Some residents said they suspect the burglar drives around during the day to see which homes have open windows and then returns to see if the homeowners remembered to lock them.
NBC 5's Ellen Goldberg contributed to this report.