Groberg's mission on Aug. 8, 2012, seemed clear cut: escort then-Col. James Mingus, who is now a brigadier general, as well as some high ranking Afghanistan leaders to attend a Kunar province security meeting with an Afghan provincial governor.
He'd done these kinds of escort missions before, usually without a hitch.
But that day was different. Things felt "eerie" and "odd".
He and Sgt. 1st Class Brian Brink, who was also part of the escort mission, shared that sense of foreboding.
Their hunch proved right when several motorcycles whipped around a corner. The riders approached in the direction of the unit then got off the bikes and seemed to leave.
Then Groberg saw a man on his left walking backwards toward them. When the man turned around, Groberg noticed he was wearing a vest.
Groberg quickly assessed the situation and realized "he's the threat." He couldn't shoot the man because he didn't know the full scope of the situation, plus the man was armed.
"So I hit him," Groberg said adding that he pushed the man further away and grabbed the man by the vest. He and Sgt. Andrew Mahoney tackled him as well in an attempt to get him away from the rest of the detail.
Sometime during this skirmish, the man's vest detonated. Command Sgt. Maj. Kevin J. Griffin, Maj. Thomas E. Kennedy, Air Force Maj. Walter D. Gray and Ragaei Abdelfattah, a U.S. Agency for International Development foreign service officer, were all killed in the blast.