Deputy Dennis Wallace was investigating a suspicious van at the Fox Grove Fishing Access Sunday morning when he was fatally shot by David Machado, officials said.

Stanislaus County Sheriff's detectives are still working out the details leading up to the shooting, but the department does know this: The 37-year-old Machado was a known criminal with preexisting warrants out for his arrest. Wallace, 53, notified dispatch before approaching the suspect, stating that Machado was "possibly armed with a firearm" before asking for backup, according to officials.

Minutes later, Wallace was found by responding officers lying down near his patrol car with gunshot wounds to the head. He was pronounced dead at the hospital.

Everything before that, however, is still unknown, according to the sheriff's department.

“Just like families who lose loved ones, we’ve lost someone special to us," Sheriff Adam Christianson said about Wallace.

The 20-year veteran with the Stanislaus County Sheriff's Department was the ninth California officer to die by gunfire in the line of duty this year, and the 58th in the country, according to the non-profit Officer Down Memorial Page.

The non-profit has been tracking officer deaths since 1996, and have numbers dating back to the 1790s thanks to the National Law Enforcement Officer's Memorial Fund. According to the data, officer deaths are on the rise in 2016, and have already surpassed the previous year's 41 deaths by gunfire.

But there have been other causes of death, too.

California Highway Patrol Officer Nathan Taylor, a 6-year veteran, was killed by a motorist in March 2016, while he was directing traffic on I-80 near Donner Summit, according to police. Taylor was one of 48 officers to die in a "traffic-related" incident in the 2016, another number that has already surpassed its previous year's number.

Here's a broader look at the numbers since 2010:

  • 2016:
    • Firearms-related: 58
    • Traffic-related: 48
    • Other causes: 15
    • California: 11
  • 2015:
    • Firearms-related: 41
    • Traffic-related: 47
    • Other causes: 42
    • California: 6
  • 2014:
    • Firearms-related: 50
    • Traffic-related: 51
    • Other causes: 45
    • California: 16
  • 2013:
    • Firearms-related: 33
    • Traffic-related: 48
    • Other causes: 43
    • California: 10
  • 2012:
    • Firearms-related: 50
    • Traffic-related: 50
    • Other causes: 39
    • California: 2
  • 2011:
    • Firearms-related: 73
    • Traffic-related: 60
    • Other causes: 48
    • California: 10
  • 2010:
    • Firearms-related: 61
    • Traffic-related: 73
    • Other causes: 43
    • California: 12

In Taylor's case, the death was an accident caused by icy roads and snowy conditions. For Wallace, however, police say he was "executed."

Machado was arrested by Lindsay police officers hours later after he robbed a convenience store with a gun, and tried to steal a woman's purse.

Officials with the Stanislaus County Sheriff's Department are looking to speak with anyone who has information about Machado's whereabouts before the shooting to help build a timeline of the incident. If you have any information, contact the department at (209) 525-7073.