SPOTSYLVANIA, Va. -- Undercover sex is getting the OK from a Virginia sheriff.

Spotsylvania County Sheriff Howard Smith said he stands by the practice of allowing detectives to receive sexual services in the course of their investigations so they can catch suspects in the act.

Court documents show that four times last month, county detectives allowed women at a massage parlor to perform sex acts on them. In one case, a lawman left a $350 tip. Smith acknowledged the practice is not new.

Smith told The Washington Post that only unmarried detectives are allowed to do the under-the-covers work.

He said actual sex acts are needed to help win prostitution convictions.

"If I thought we could get the conviction without that, we wouldn't allow it," Smith told the newspaper. "If you want to make them, this has to be done."

He said most prostitutes are careful not to say anything incriminating, which makes sexual contact necessary

Several police officials and legal observers say the practice has been tried by other agencies across the country, but they knew of none that still permit sexual contact with suspects as part of prostitution investigations. But many police agencies across the country have banned sexual contact between investigators and suspects.

When police used similar tactics in the past in Montgomery County, Md., the charges ended up being dropped.