(CNN) The sheriff's sergeant who initially responded to last month's mass shooting at the Borderline Bar and Grill in Thousand Oaks, California, was fatally shot by gunfire from a California Highway Patrol officer, officials said Friday.

Sgt. Ron Helus was struck five times by gunfire from the suspect, Ian David Long, according to Ventura County Sheriff Bill Ayub, but was hit by a sixth bullet from a CHP officer's rifle.

Helus could have potentially survived the five wounds from Long's weapon, but the sixth bullet, fired by the CHP officer who entered the bar with Helus, proved fatal. It struck Helus in the chest and his heart, according to Dr. Christopher Young, the Ventura County medical examiner.

"This is sad news and a tragedy," Young said, "but ultimately this was the most severe injury sustained."

Young told reporters officials were aware of Helus' injury but that they waited to release the information before getting confirmation from FBI ballistics analysis.

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