Minutes after Attorney General Eric Holder on Tuesday called a sharp rise in the number of cops killed on the job "simply unacceptable" and vowed action, a young Athens, Ga., police officer died after getting into a gunfight with a grudge-carrying carjacker.

Coming off a year that saw an increase in the number of police officers killed, especially by gunfire, the first three months of 2011 have seen another dramatic spike as the "officer down" call has gone out in Wisconsin, Michigan, Florida, Georgia, and other states.

Mr. Holder's vow – at a meeting with police chiefs at the Justice Department in Washington – to fight back underscores that many in the US police community are worried about a looming "war on cops" in line with what some experts say is declining respect for law and order – and the US government.

Arizona shooting: US has lots of guns, but it's not alone

The rise of right-wing movements like the "sovereign citizens" – two of whose members were involved in a double police homicide in 2010 – is part of the equation, as is the expanding availability of guns and the growing willingness of armed citizens to use them. But a steady increase in the number of justified homicides by police officers in recent years has also served to "heighten tension" between cops and the communities they serve, says Al Blumstein, a criminal justice expert at Carnegie Mellon University in Pittsburgh.

Interestingly, the spike in police officer deaths does not correspond with violent crimes and homicides in the rest of society, which have steadily dwindled over the past decade from around 8 homicides per 100,000 Americans to fewer than 5 per 100,000 last year. So what gives?

'Exceedingly hostile' malcontents

"There is a contingent of malcontents out there who are exceedingly hostile," says Rich Roberts, a spokesman for the International Union of Police Associations. "It's a really complex phenomenon in that it's a whole combination of factors where on one end you've got people like sovereign citizens, who are actually deliberately targeting police, as opposed to your garden variety bad guy who's carrying a gun and will not hesitate to use it."

Twenty-four police officers and three federal agents already have been shot in the line of duty in 2011, compared with 15 during the same period in 2010. The total number of police deaths rose by 37 percent from 2009 to 2010, leading many officers to perceive that "there's a war on cops going on," Mr. Roberts said in January after 11 police were shot in a 24-hour period.

More recently, 20-something officer Craig Birkholz was killed during a home standoff in Fond du Lac, Wis., with a disturbed Iraq War veteran. And this month, a US marshal was killed and several officers hurt during a standoff near St. Louis.

Carnegie Mellon's Mr. Blumstein attributes the raised tensions and increased rate of violence to a combination of the easier availability of guns and what James Alan Fox, a criminologist at Northeastern University in Boston, has described as an emerging "shoot first" mentality by both police officers and armed citizens.

Tuesday's shooting in Athens, Ga., for example, may have been part of a long-simmering personal vendetta between the alleged shooter and local police. The brother of alleged shooter Jamie Hood was gunned down by Athens-Clarke County police in 2001 after police say he drew a gun.

Increase in 'justifiable homicides'

One barometer of the shoot-first mentality among both law enforcement officials and civilians has been an increase in the number of "justifiable homicides," killings that have not led to prosecutions. Between 2005 and 2009, the number of justifiable homicides by private citizens rose about 33 percent nationwide, from 196 to 261, according to FBI statistics, while justifiable homicides by police hit 406 in 2009 – the largest number since the all-time high of 462 in 1994 – after having risen steadily over the previous decade.

Blumstein attributes the increased number of shootings by police to their being perhaps "more sensitive to more ... inappropriate people out there carrying guns." He said police "may be more defensive, more reactive, which can lead to an escalation of an incident from simply a confrontation to a shootout."

Gun rights advocates point out that overall crime rates and homicides tend to be lower in so-called right-to-carry states and states with home defense "castle doctrines."

In his meeting with police chiefs Tuesday, Holder, America's top cop, stated that "nothing was off the table" in the debate about how to reduce the number of gun-related police fatalities. Whether that means new gun control legislation, as the Obama administration has recently promised, or more funding to cash-strapped police departments remains to be seen.

Arizona shooting: US has lots of guns, but it's not alone