(CNN) — Three days after a golf pro was shot dead on an Atlanta-area course and two others were found dead in a pickup truck there, police still are hunting for clues to whoever killed them.

And members of the country club where Gene Siller was shot dead remain in the dark about why the killings happened, a friend of Siller’s said Tuesday.

“This doesn’t make any sense,” Brian Katrek, a member of Pinetree Country Club in Kennesaw and an anchor of SiriusXM PGA Tour Radio, told CNN’s “New Day.”

“I think the reaction from members right now is still one of pretty profound shock.”

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 two other men in the truck’s bed — both of whom also had been shot, police said.

Someone had driven to the green in the truck — a white Ram 3500 pickup — and shot Siller when Siller arrived to see what was going on, a member of the club told CNN affiliate WXIA. The shooter then fled, WXIA reported.

One of the slain men was Paul Pierson the registered owner of the Ram 3500, police said. The name of the other slain man was not released.

Police have said they’re trying to determine what happened and have not released the name of a suspect.

Investigators told CNN they are asking residents to check their doorbell video for any clues.

The three people slain were among of at least 150 people killed by gun violence in more than 400 shootings across the US during the Fourth of July weekend.

Siller leaves behind a wife and two children

The Georgia State Golf Association expressed its condolences for Siller’s death. “All of us at the GSGA are deeply saddened by the tragic events that occurred earlier today at Pinetree CC. Our thoughts and prayers are with Gene Siller’s family and friends,” the association tweeted.

Siller, 41, leaves behind a wife and two children, ages 6 and 7, according to the Pinetree Country Club.

“Tragedy has stricken the Georgia Section PGA in the loss of our Member, Gene Siller. Thoughts and prayers for his family and the Pinetree Country Club family,” Georgia’s Professional Golfers’ Association tweeted.

PGA of America President Jim Richerson also issued a statement: “We are truly heartbroken to hear about the senseless murder that took place yesterday at Pine Tree Country Club in Georgia that took the life of PGA member Gene Siller,” the statement said. “PGA of America sends our thoughts, prayers and deepest sympathy to his family, club and the Georgia PGA Community.”

Sebastian Schutte, a friend of Siller’s, said the community was in shock.

“It didn’t hit me until later that this happened at our country club,” he told CNN on Monday. “I still can’t believe it.”

He said Siller was well-liked and “treated everyone with respect.”

Siller’s family set up a GoFundMe page to help with finances.

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