As of today, Arlington County has been homicide-free for exactly two years. It’s the first time Arlington has gone this long without a homicide in the 72-year history of the Arlington County Police Department.

“Reaching this mark is only possible through a combination of effective policing, excellent medical care, successful prosecution and cooperating communities; all of which we have experienced in Arlington County the past two years,” police chief M. Douglas Scott said in a statement.

The county has not recorded a single homicide since March 14, 2010, when a 20-year-old man was stabbed to death in the Lyon Park neighborhood. The suspect in the case later pleaded guilty to second degree murder.

Amid the celebration of the murder-free milestone, however, there’s some concern within the department that there are not enough cops on the street to ensure that the recent, broader drop in crime continues. Despite a growing population and new post-9/11 anti-terrorism responsibilities, Arlington’s police force has actually shrunk slightly since 2001.

Whereas there were 362 sworn officers in Fiscal Year 2001 for a population of 189,983, there are currently 359 sworn officers for a population of 213,400 in FY 2012. That means ratio of officers to every 1,000 residents is 1.68, compared to 1.91 in FY 2001. That ratio is expected to get even narrower — to 1.67 — if the current recommended FY 2013 budget is adopted. (The population is expected to grow to 215,000 while the budget doesn’t provide for any additional officers.)

By comparison, in 2010 Alexandria’s officer/resident ratio was 2.19, and D.C.’s ratio was 6.52, according to a law enforcement source. Just to match Alexandria’s ratio, Arlington would need to hire more than 100 new officers.

“Our numbers are extremely low,” a police official told ARLnow.com. “Obviously we’re working efficiently, I don’t think anybody would deny that… [but] at some point in time, I’m not sure how much lower our ratio can go” without a corresponding increase in crime.