On Thursday, Virginia State Police trooper Chad P. Dermyer was participating in a training exercise at a Richmond bus station when he approached a man just inside the facility's front doors. 

Dermyer, a 37-year-old from Michigan, had just begun speaking to him when the man pulled out a handgun and fired multiple rounds at the trooper, police officials said. Two other troopers returned fire and killed the gunman, according to the state police. Dermyer was later pronounced dead at a local hospital.

His death contributes to a grim, growing toll: During the first three months of 2016, the number of police officers killed in shootings more than doubled from the same period last year.

Dermyer was the 16th law enforcement officer shot and killed this year, up from seven such deaths at the same point in 2015, according to the National Law Enforcement Memorial Fund, a nonprofit group that tracks line-of-duty deaths.

The list of officers slain this year includes Jacai Colson, the Prince George's County officer who was killed during a shootout outside a police station. Police said that Colson, who was wearing street clothes, was shot and killed by another officer who mistook him for an attacker.

All told, the memorial fund's database on police officer deaths shows a slight increase overall. Including Dermyer, there were 30 officers killed in the first three months of 2016, up from 27 deaths a year earlier. While fatal shootings have surged, the number of officers who died in traffic accidents or from other causes, such as heart attacks, has declined.

Last year, the number of officers who died increased from the year before, an uptick that was due to things other than gunfire.

According to the memorial fund, the number of officers fatally shot declined (falling to 42 from 49), as did the number killed in what the memorial fund called "felonious incidents" (falling to 52 from 61). But the death toll rose to 124 deaths from 119 a year earlier because of spikes in traffic accidents and job-related illnesses.

Overall, the number of officers fatally shot each year nationwide is down from what it has been in recent decades. In the 1970s, an average of 127 officers were shot and killed each year; between 2000 and 2009, an average of 57 officers were fatally shot each year.

Even as the number of deaths has fallen, current and former officers, along with relatives of law enforcement officials, have said they are increasingly anxious amid a greater focus on police officers who use deadly force.

The Washington Post reported Friday that a fifth of the police officers who fatally shot someone last year were not identified. Many reasons were offered by officials, including the suggestion that names should not be released while investigations were ongoing; in other cases, police said they weren't revealing the names because of safety concerns.

Last year, police officers fatally shot 990 people, the vast majority of them individuals armed with guns or people who had attacked or threatened others, according to The Post's database tracking these shootings. As of Friday, officers have shot and killed more than 250 people.

The law enforcement officers who have been shot and killed so far in 2016 were killed in a variety of incidents: A sheriff's deputy in Colorado was killed while serving an eviction notice, a Mississippi state narcotics officer was slain when a home standoff turned violent. In one weekend, a Utah officer was killed after someone fled a car crash, while an Ohio officer's death came after police received a 911 call about a man targeting police.

This tally does not include officers who were wounded but survived, such as the three Chicago police officers injured during a drug investigation last month. Authorities have also described ambushes that ended with injuries that were not fatal, like the case involving an officer in Miami Gardens, Florida, who police said was shot while sitting in a parking lot.

In perhaps the highest-profile example of such an attack this year, a Philadelphia officer survived being ambushed by a man who ran up to his car and opened fire; authorities later said the attacker told them he had pledged his loyalty to the Islamic State.

"Some of these attacks have been launched by Islamic extremists or sovereign citizen types with a hatred of our government; others are being carried out by mentally deranged or coldblooded criminals who see police as the enemy," Craig W. Floyd, chief executive of the memorial fund, said in a statement last month. "In all cases, our officers are being targeted simply because of the badge that they wear and the job that they do."

Officials have been worried about ambush attacks in recent years, something that has continued into this year due to ambushes that occurred in the first months of 2016.

The Justice Department released a study last year that looked at ambushes of law enforcement officers between 1990 and 2013, finding that while the number of ambushes each year remained steady, the proportion of fatal attacks attributed to these incidents was increasing.