NORTH TEXAS (CBSDFW.COM) – A North Texas family who dealt with tragedy after the July 7th police ambush in Dallas is grieving again.

Officials in Navarro County have confirmed District Attorney R. Lowell Thompson has died unexpectedly.

The Navarro County Office of Emergency Management announced Thompson’s death on Twitter, saying, in part –

“His sudden passing this morning is a shock to us all. Please keep the entire family in your thoughts and prayers.”

Lowell Thompson is the older brother of Brent Thompson, the Dallas Area Rapid Transit (DART) police officer shot and killed more than two years ago when a sniper opened fire on police in downtown Dallas.

Officials with the District Attorney’s Office have not released any information and it isn’t yet know exactly how Lowell Thompson died.