Two men wearing masks and gloves entered an upscale yoga clothing store in downtown Bethesda after closing hours this weekend, killed a worker and sexually assaulted another, officials said Saturday. Detectives think the attack began as a robbery about 10 p.m. Friday along the high-end Bethesda Row shopping district.

The assault victim, who is expected to survive, was found bound in the back of the store Saturday morning. She was hospitalized and has been talking with detectives.

Police declined to say how the homicide victim, identified as 30-year-old Jayna T. Murray, of Arlington, was killed. But law enforcement sources confirmed a horrific, bloody scene inside Lululemon Athletica, part of a chain of stores that began popping up across the country a few years ago. The stores sell yoga and sports clothing and are designed to give shoppers a sense of calm.

Violent crime is exceedingly rare in Bethesda's central business district; law enforcement and government officials couldn't recall a recent homicide.

"We're all stunned. No one can remember another murder in the last 20 years," said Ken Hartman, director of the Bethesda-Chevy Chase Regional Services Center, a government office for the area.

The Bethesda store sits between the Papery, a stationery store, and an Apple retail store that has been buzzing this weekend with its hot new product, the iPad 2.

It was unclear how long the assailants were inside the store.

The two victims had closed the store at 9 p.m. Friday and left a short time later, police said. One of them realized that she had left something behind and didn't have the means to get back inside, police said. She called her co-worker, who met her at the store and let her inside, leaving the door unlocked.

Detectives think that the men - dressed all in black with faces and hands covered - entered a short time later, police said.

Because the intruders were covered, police have come up with only limited descriptions, with one being 6 feet tall and the other a little over 5-foot-3, police said.

On Saturday morning, a female worker arrived to open the store, according to a police spokesman. She heard a faint noise in the back of the store, retreated and called a man who was outside to come into the store, police said.

This man went farther into the store and saw what he thought were two bodies in the back of the store. Police were called.