JEFFERSON COUNTY, Colo. -- A woman who stepped out onto of her patio Monday morning for some fresh air was dragged back into her apartment, punched, stripped and then sexually assaulted, the Jefferson County Sheriff's Office said.

The attack occurred at about 2:10 a.m. in the 7400 block of South Quail Circle, near Ken Caryl Avenue and Simms Street.

The woman told the deputies she could not sleep so she went outside to the patio just as she had in past nights. Just as she was about to close the patio door, a man grabbed her from behind and forced her back inside the apartment, she said.

He pulled off her clothes, sexually assaulted her and then left the apartment through the front door, the woman said.

"Our biggest concern with this is that the suspect was waiting for the victim," said Jim Shires, of the Jefferson County Sheriff's Office.

She described her attacker as white, 6 feet tall, with a large build and big waistline. He was wearing black sweat pants, a black long-sleeved shirt and had a hood over his face.

Monday afternoon deputies patrolled the condo complex where the attack occured. It was the first time many residents learned of the assault.

"It is definitely scary," said Ericka Delong, who lives in the complex. "That is just horrible. I would never have imagined this in a gated comunity like this."

The sheriff’s office is advising everyone, no matter where they live, to make sure all of their doors and windows are secured before going to bed. Also, people should turn lights on before stepping outside in the dark. Other protective measures include motion-sensor lights, alarms and Neighborhood Watch programs.

Anyone with information about this crime is urged to contact the Jefferson County Sheriff's Office tip line at 303-271-5612.