Law enforcement officers and emergency service personnel converge on the scene of the shooting in downtown Williamson, W.Va., Wednesday. (Kyle Lovern/AP)

Law enforcement officials already on edge after the killings of two Texas prosecutors and a Colorado prison director got more reasons to worry Wednesday, as a West Virginia sheriff was fatally shot, and authorities in this northeastern Texas community said they arrested a local man for threatening another county official.

It is uncertain whether the killings are connected or merely coincidental events in dangerous professions. Authorities here said the arrest of Nick Morale, 56, who phoned in a threat to a police tip line, was not related to the killings of Kaufman County District Attorney Mike McLelland and his wife, Cynthia, over the weekend, or that of Assistant District Attorney Mark Hasse on Jan. 31.

Still, the news has heightened alarm among law enforcement officials, especially in this rural county, where judges are being escorted by armed guards to and from work, sheriff’s cars are parked outside the new district attorney’s house, and secretaries in the county courthouse have been given bulletproof vests.

“I’m not going to live in fear,” Kaufman County Judge Bruce Wood said Tuesday. “But I’m not stupid either. We’re being very careful about security for all officials, not just judges.”

The killings of McLelland and Hasse have drawn at least several dozen FBI agents, as well as U.S. Marshals and Texas Rangers, to the area to assist the local sheriff’s office. The FBI sent a Computer Analysis Response Team, a mobile forensics laboratory that analyzes computers and other digital items seized in searches.

Mingo County, W.Va., Sheriff Eugene Crum was gunned down Wednesday in the spot where he usually parked and ate lunch. (Rachel Baldwin/AP)

“It’s gotten a lot of attention,” said one federal law enforcement official who spoke on the condition of anonymity because the investigation is underway. “We have prosecutors who are being murdered. It’s very serious. You can’t have the word get out to people that you can just murder prosecutors and they won’t put you in jail.”

It is unclear whether investigators have any strong leads in the killings here. One focus has been the Aryan Brotherhood of Texas, a violent prison gang involved in criminal enterprises, although some federal law enforcement officials in recent interviews have expressed caution about whether the group had any role in the Kaufman County killings, saying such a connection is premature.

McLelland prosecuted a case last year against an Aryan Brotherhood member convicted of kidnapping, assault and directing gang activities, among other charges. And in November, federal prosecutors in Houston announced indictments against 34 members of the gang, including senior leaders, after a multi-agency inquiry that involved the county district attorney’s office.

On Monday, Assistant U.S. Attorney Jay Hileman, the lead federal prosecutor in the case, announced in an e-mail to defense attorneys that he was withdrawing because of “security concerns,” said Richard Ely, who represents one of the defendants. Ely said the e-mail was not specific.

In West Virginia, Mingo County Sheriff Eugene Crum, known for his tough stand against the drug trade, was fatally shot Wednesday in the place where he usually parks his car for lunch, about a block from the county courthouse, according to the Associated Press. The local courthouse was evacuated and streets were blocked off — a scene not unlike the one that unfolded here in January, when Hasse was shot as he walked from a parking lot to the courthouse on a shaded square.

The death rates for law enforcement officers nationally have fluctuated over time, with the most dangerous period coming in the 1970s. Overall, deaths of officers in the line of duty spiked from 122 in 2009 to 165 in 2011 and dropped to 129 last year, according to the D.C.-based National Law Enforcement Officers Memorial Fund.

Over the past three years, however, premeditated attacks on law enforcement officials have spiked, according to research conducted by Glenn McGovern, a senior investigator for the district attorney’s office in Santa Clara County, Calif., who has written two books on the subject.

Fifteen targeted attacks occurred in that time frame, six in which one or more people were killed, said McGovern, who equated the recent level of violence with 1980s Mafia killings in Sicily and recent drug-related homicides in Mexico. During a comparable period from 2000 to 2003, McGovern said, there were six such attacks. He could not explain the increase.

Markon reported from Washington.