Police in an affluent Washington suburb say a co-worker killed a woman found dead inside a yoga clothing store in Bethesda, Md., recently, then made up a story about the two being attacked by masked men.

The suspect, Brittany Norwood, 27, told police March 12 that two masked men had entered the Lululemon Athletica store in Bethesda the night before and attacked and sexually assaulted her and her co-worker, Jayna Murray, 30, of Arlington, Va. The next morning, another store employee found Murray dead inside the shop and Norwood injured and bound.

But after six days of investigation, police now believe that neither woman was sexually assaulted and that Norwood killed Murray following some sort of dispute, according to J. Thomas Manger, the Montgomery County police chief. Norwood was arrested Friday and was charged with first-degree murder, the chief said at a news conference. She is being held at the Montgomery County detention center in Rockville.

Manger said police were initially inclined to believe Norwood’s account. They solicited tips from the public, offered a reward for information that could help solve the case and even conducted surveillance on a person of interest. But her description of the attack didn’t mesh with forensics and medical evidence that police recovered, Manger said.

In fact, Manger said, “It took us in another direction.”

It was not immediately clear if Norwood had a lawyer, and police didn’t say where she lived, though a police official says she has a Washington state address. Manger was due in court Monday.

Manger said police found only two sets of footprints inside the store, contradicting accounts that more people were inside, and said that workers at the adjacent Apple store reported hearing two women arguing.

He also said that blood and forensics evidence believed to be connected to Norwood were found inside Murray’s car several blocks from the store. He wouldn’t further describe the evidence.

Police confronted Norwood on Friday, said Manger, but he declined to discuss how she responded.

Based on Norwood’s account, authorities initially said the two co-workers returned to the store after it closed on the night of March 11 because one of them said she had left something inside. Police believe Norwood got Murray to come back to the store by telling her she had to retrieve something and needed help.

Authorities said Murray died of blunt force trauma and stab wounds.

Police say there’s no evidence that anyone else was involved in the killing, but Manger said the investigation is continuing.

The crime rattled Bethesda, home to many of the capital’s political and business leaders and where violent crime is rare.