HOUSTON -- An elderly northwest Houston woman was attacked and robbed by a man who had offered to help her seconds before, KPRC Local 2 reported Thursday.

Rosalie Dahl, 87, had just finished doing her laundry when a stranger approached her as she left a neighborhood Laundromat on Wednesday morning.

She said the man came up to her as she put clothes in her vehicle.

"He says, 'You need some help?'" she said. "He knocked me down on the sidewalk, grabbed my purse."

Dahl suffered cuts and bruises on her face and broke her glasses.

"My arm hurts real bad, and I couldn't sleep last night," Dahl said.

Houston police said it was a crime of opportunity. Criminals often case out parking lots searching for women with purses, elderly residents or anyone who looks vulnerable, officials said.

"Always be aware of your surroundings. If you park in a parking lot, make sure it's well-lit. Make sure you're not parked next to large vehicles where somebody might come out of that vehicle and attack you," HPD spokeswoman Johanna Abad said.

Police also said that if someone tries to grab a purse, the woman should give it up willingly and not fight. Also, women should limit how much information and credit cards they carry.

Investigators did not have a description of Dahl's attacker. Her purse and driver's license were found discarded along the Gulf Freeway.