SEATTLE (AP) — Federal prosecutors have decided to drop child pornography charges against a Washington teacher after the Justice Department refused to disclose information about a software weakness it exploited during an investigation last year.

Charges against Vancouver teacher Jay Michaud in U.S. District Court in Seattle were dropped Monday.

Michaud was arrested in July 2015 and accused of downloading child pornography from a website called Playpen.

People on the website, which was actually operated by the FBI, used a special web browser called Tor to protect their identities, but FBI agents exploited unknown weaknesses in that browser to identify suspects.

A judge in Michaud's case ordered the FBI to disclose to the defense parts of their hacking process but the government refused.

KGV-TV reports that a school district spokeswoman says Michaud hasn't returned to work there.