Violent crime in Prince William County rose in 2012, even as the overall crime rate dropped for the fifth straight year, according to the police department’s annual report released at a news conference on Tuesday.

The county had two murders in 2012, the lowest in decades. The most serious crimes — including rapes, aggravated assaults and robbery — rose 8.96 percent, primarily driven by a 46 percent spike in rapes over 2011. Rapes that occurred in past years, but are counted in the year they are reported, accounted for 4.1 percent of the almost 9 percent increase in the violent crime rate.

The number of reported rapes climbed from 46 in 2011 to 67 last year, the report showed.

Police Chief Stephan M. Hudson credited public education efforts with more victims feeling that they could come forward with crimes that, in some cases, took place years ago.

“Overall, the general knowledge of the public … has been helpful in showing that it is safe and appropriate to come forward,” he said.

The overall crime rate drop despite population growth is a continuing positive trend, Hudson said. “It has to do with people being more invested and engaged in their community,” he said. The overall crime rate was 17.04 crimes per 1,000 citizens. Aggravated assault, burglaries and motor vehicle thefts all decreased in 2012, according to the report.

Hudson said that any increase in violent crime is concerning. He said he is particularly concerned about the number of fatal traffic deaths — 18 — including pedestrians killed while crossing the street. Eight pedestrians were killed in fatal collisions. In seven of those deaths, the pedestrian being intoxicated was a factor, the report said.

Most of those deaths occurred where a crosswalk could have been used, police said.

“People have to understand when and where it is safe to cross,” Hudson said.

He also said that the department would examine and look to implement new tactics when it comes to robberies, which climbed 16 percent. That analysis has not yet taken place, he said.

Prince William is one of the few localities in the nation that looks to enforce illegal immigration locally through a partnership with federal authorities called a 287 (g) agreement. Undocumented immigrants flagged by the county accounted for 70, or 3.9 percent, of violent crime offenders in 2012, according to the report.

In December, the federal Department of Immigration and Customs Enforcement announced that area task forces on the street, who investigate the presence of undocumented immigrants, would no longer be able to operate under the agreement. Prince William disbanded its six-member unit, Hudson said.

The program was allowed to continue at county jails, where officials check the immigration status of every person arrested under a local policy passed in 2008.

The street level unit that handled the immigration-related work always had various other investigative duties, Hudson said. As a result, the chief said, ICE’s new policy “has had no real change on the way we do business.”