Sombath Somphone. Pic: AP.

WASHINGTON (AP) — Five hundred days after the most prominent civil rights advocate in Laos went missing at a traffic police checkpoint in the capital Vientiane, his wife says she remains completely in the dark about what happened to him.

Sombath Somphone’s disappearance was recorded on closed circuit television, which should have helped investigators. The footage shows the activist being escorted by two men to a pickup truck and driven away.

But Laos has released scant information, and the apparent abduction has sent a chilling message to civil society in the one-party state.

His wife, Ng Shui-Meng , is in Washington to urge the Obama administration and Congress to press the Lao government to resolve the case.

Before the disappearance, the 63-year-old Sombath had been diagnosed with prostate cancer.