Fairfax County police said Monday they now believe the July disappearance of a Springfield man may be the result of foul play.

Oscar Velasco Montano, 30, was last seen on July 9 in Tysons Corner, where he was working at an office building on International Drive near Route 7. He never returned home, and his car was found near his workplace six days later.

“Initially, there was nothing to indicate foul play,” said Officer Tawny Wright, a spokeswoman for the Fairfax County police. “Recently, detectives have found reason to believe his disappearance is not voluntary.”

Wright declined to discuss the new evidence, which is detailed in a search warrant that has not been unsealed.

Montano’s family filed a missing persons report on July 11. At the time, his family said there was no activity on his bank account and he had not used either of his two cellphones.

The family has set up a Facebook page to help locate him.

Anyone with information about him is asked to call Fairfax County police at 703-691-2131 or Crime Solvers at 1-866-411-TIPS.