Though Fairfax County police are combing the streets searching for those involved in a sexual assault last week in Merrifield, they report the number of such attacks investigated by the agency have actually gone down in recent years.

Over the past three years, there has been a steady decrease in sexual assaults in Fairfax County as well as the state, according to the agency. In 2011, Fairfax County police investigated 251 forcible sex offenses, down from 320 investigations in 2010.

FCPD spokesman Bud Walker said in 2012,  the department has investigated 154 forcible sex offenses — “at this time last year, we had investigated 160," he said.

The Aug. 19 sexual assault in Merrifield was the second reported in the area since May, when a 50-year-old woman was attacked by two men around 1 a.m. in the 2400 block of Gallows Road near the W&OD Trail. The woman was hospitalized after the attack.

Walker said there are no leads in the most recent attack. Police do not know the cause of the decrease, but Corrine Geller, a spokeswoman for the Virginia State Police, said her agency has investigated 50 forcible sexual assaults through June 30 of this year. VSP investigated 211 forcible sexual assaults and assisted other state agencies in 78 other investigations in 2011.

With nine full-time detectives and one lieutenant, Walker said Fairfax County's Sex Crimes Unit has seen the number of cases they investigate decrease. He said the unit has not investigated a forcible sexual assault that ended in death.

Geller said VSP has several violent crimes investigators designated to the seven field offices the agency maintains throughout the Commonwealth. She said some of those investigators have received special training to deal with victims of a sex crime. In today’s technology era, Geller said VSP has also developed a unit to handle online sex-related crimes.

“We also have agents assigned to our High-Tech Crimes Division who trained in investigating sex crimes associated with online cases,” Geller said.