The shooting death of David Carlson more than four months ago was a shattering and frightening moment for his partner, David Schallhammer. It was just a few days before Christmas that Schallhammer discovered Carlson, 52, in their garage, bleeding from the head. His wallet was out, but no money was missing. His cellphone had been taken.

Though police have speculated from the beginning that Carlson died in a robbery gone bad, Schallhammer fears that the violence might not have been random. He was scared for his safety, he said, and wanted to avoid doing anything that might antagonize the shooter.

But with no arrests in the case and the investigation growing cold, Schallhammer has found resolve.

“I’m at the point where I don’t give a damn,” Schallhammer said. “I’ve got to do something.”

For more than an hour on the evening of May 1, Schallhammer went door to door distributing flyers and looking for leads that may help solve the case. He sat down with a television reporter and issued a tearful plea for help. One of his greatest concerns is that his partner’s murder will become “old news.”

“You try not to lose hope, but when it’s four and a half months out … ,” Schallhammer said, his voice trailing off.

In canvassing the area, Schallhammer was joined by a handful of officers from the police department, a pair of friends and three volunteers with Cook County Crime Stoppers, a nonprofit agency called in to assist with the effort. Crime Stoppers is offering a $1,000 cash reward for information leading to an arrest.

George McDade, chairman of the board of directors for Crime Stoppers, was among those pounding the pavement in Forest Park earlier this month. For this case, McDade said his group is focusing on the two el stations that are within walking distance of Schallhammer’s home on the 500 block of Hannah Avenue.

The transit stations offered the shooter an easy escape, especially in the early evening hours when the train stations would be busy. Investigators also recovered a critical clue that points them to the el.

“I think we’re targeting the right audience,” McDade said.

When authorities responded to the shooting on Thursday, Dec. 20, they saw that Carlson’s cellphone had been stolen. They began monitoring the number and almost immediately learned that calls were being placed. They found the phone on a Red Line train and brought three people in for questioning, only to learn that the trio had discovered the phone abandoned on the train.

McDade is hoping that by returning to the el stations on a Thursday evening, they’ll find someone who can lead them to the shooter.

In the months following Carlson’s death, Sgt. Mike Keating of the Forest Park police has maintained almost weekly contact with Schallhammer. In Schallhammer, Keating has seen a range of emotions-from frustration to anger to immeasurable sadness. While knocking on doors and randomly asking people on the street for their help, Keating admits it has been a frustrating investigation.

The discovery of the cellphone was an elating moment, he said, only to have that dashed after speaking with the people on the train. Video surveillance turned over by the Chicago Transit Authority hasn’t yet yielded anything promising and Keating said it’s incredibly unusual that the shell casing from the .25 caliber bullet wasn’t recovered at the scene. It’s possible, he said, that the gun malfunctioned and didn’t expel the casing, or that it somehow got hung up on the shooter’s clothing.

“That’s the way this investigation has worked,” Keating said.

Schallhammer has nothing but praise for the police department’s handling of his partner’s case, and in particular, Keating. His frustration is with the state, he said, which isn’t expected to return any forensics to local investigators for at least another six weeks.

“He’s a good man. I have no doubt about that,” Schallhammer said of the sergeant in charge. “If it can be solved, he’ll do it.”

Keating confirmed that despite steady pressure from his office, the state has yet to reveal its findings.

In the hours immediately after the shooting, Schallhammer became the first suspect. He shrugs, acknowledging the reality of what police often discover in such cases, though he said it should have become apparent quickly that he did not kill his partner of more than 30 years. His voice fractures with emotion when he discusses his loss.

McDade said he insists that members of Carlson’s family and their friends participate anytime his organization distributes flyers or otherwise reaches out to the public. The search becomes more meaningful to everyone involved, he said, and can have a healing effect on the survivors.

When Schallhammer stops a pair of elderly men on a street corner to give them a flyer, he doesn’t mention his relationship to the man pictured. His voice is steady and he looks both men in the eye. One says that he remembers the shooting and, in taking a flyer, wishes Schallhammer luck.

“It is helpful,” Schallhammer said.

Anyone with information about the case is encouraged to call the Forest Park police at 708-366-2425 or Cook County Crime Stoppers at 1-800-535-7867.