Siller, 41, and the other two men were discovered Saturday at the Pinetree Country Club in Kennesaw, Georgia, according to police.
One of the slain men was identified by police as Paul Pierson. The other man remains unidentified.
Siller, Pinetree’s director of golf, was found unresponsive with an “apparent gunshot wound to the head” and was pronounced dead at the scene, police said. Pierson and the other victim also suffered gunshot wounds.
Investigators have not yet released the name of a suspect and say they are following leads to determine why the shooting happened.
But in the days following the deaths, some information has been released. Here is what we know:
Cobb County police said they were called to a report of a person shot around 2:20 p.m. Saturday and found Siller — the club’s director of golf — shot in the head near the green of the course’s 10th hole.
A truck was on the green, and officers found the bodies of the two other men in the truck’s bed — both of whom also had been shot, police said.
Pierson was the registered owner of the truck, police said.
Pierson and the other slain man “appear to have no relation to the location at all,” Cobb County police said Tuesday.
Police said Tuesday they believe Siller was killed “because he witnessed an active crime taking place.”
Police didn’t specify what that crime was. Investigators told CNN they are asking nearby residents to check their doorbell video for any clues.
“It does not appear he (Siller) was targeted,” but instead was killed because he “happened upon a crime in progress involving the unknown suspect and the two deceased males,” the Cobb County Police Department said in a news release.
Details for Siller’s funeral are unknown as his body remains at the Medical Examiner’s Office, the country club said in a statement Tuesday.
CNN has reached out to the Medical Examiner’s Office and has not heard back.
Who Siller leaves behind
Siller leaves behind a wife and two children, ages 6 and 7, according to the country club.
“Gene was a man of compassion, he loved everybody,” Rand Eberhard, a pastor who lives in a neighborhood near the country club and knew Siller, said. “It’s a big void that is left in our community to lose such an important guy.”
Eberhard said it would have been in Gene’s nature to help someone in need.
“He came in to check on a guy and help the guy, and this is what happens,” he said. “It’s an act of evil. It’s an act of selfishness.”
The impact on the club
Pinetree Country Club said it will reopen Wednesday, but noted staff and members are still grieving
The 10th hole will remain closed for play, club official Lou Bottino said in a letter to members.
Bottino said Siller’s wife, Ashley, and other family members visited the 10th hole where Siller was gunned down “to see where this unimaginable tragic act occurred as part of their grieving.” Bottino said Siller’s wife added flowers to a growing memorial at the 10th hole.
Members of the country club are in the dark about why the killings happened, a friend of Siller’s said Tuesday morning.
“This doesn’t make any sense,” Brian Katrek, a member of Pinetree Country Club and an anchor of SiriusXM PGA Tour Radio, told CNN’s “New Day” before Tuesday’s news release from police.
“I think the reaction from members right now is still one of pretty profound shock,” Katrek said.
CNN’s Jen Bernstein, Gregory Lemos, Pamela Kirkland, Ralph Ellis, Alaa Elassar and Claudia Dominguez contributed to this report.