Police said Belcher shot his girlfriend to death on Saturday morning at their home in Kansas City and then drove to the team's practice facility a few miles away. He then shot himself to death in the parking lot while head coach Romeo Crennel and General Manager Scott Pioli watched, police said.
"It is a sad situation, but to me, ultimately, the man committed murder," said Chiefs' fan Tony Alonzo. "The big picture is that it was a murder."
Police said Belcher's mother witnessed him shooting his girlfriend, Kasandra Perkins, 22, after they had a heated argument. Police corrected their initial report that the witness was Perkins' mother. The couple had a 3-month-old daughter.
"That is who you feel for - this 3-month-old child," fan Ira Thomas said before the game. "She has to grow up without her parents and as she gets older someone in the family will tell her what happened and that might set her back a few years."
Thomas and other fans said there was a quieter tone to the usual pre-game atmosphere on Sunday morning. Thomas expected the tragedy to affect players and fans.
"If I was a ballplayer and something like that had happened, my mind wouldn't really be in it," Thomas said.
Fan Larry Beauchamp said the NFL made the right decision to play the game on Sunday. The league announced there would be a moment of silence before the game "for all victims of domestic violence." No names would be mentioned.
Beauchamp said honouring Belcher would not be right.
"It was a tragedy, the young man obviously needed some help," Beauchamp said outside a converted school bus he painted red in the Chiefs' colour.
Another fan, Gordon Highland, wondered how Crennel would hold up after what he witnessed.
"It's got to really (be) emotional for the coach," Highland said. "You have to feel helpless, I imagine."
After discussions with the league, Chiefs Chairman and CEO Clark Hunt left the decision about whether to play with Crennel and the team, and they decided the game should go on.
"Romeo called the team captains yesterday afternoon ... and they all wanted to play the game," Hunt told ESPN on the field before the game. "And I asked coach Crennel, 'Do you think the right thing is to go forward?' and he said, 'I do. Under the circumstances, it's going to be tough.'"
Hunt visited the team to sympathise with them about how hard it would be to play.
"I wanted to tell them that I love them and I understand what they are going through," Hunt said.
"I know that the guys are going to rally around each other and they are going to come out here and give it their best," he said.
Visible tributes to Belcher outside the stadium were rare, but Kurt Gant and his son Taylor Gant, 21, displayed a sign that said RIP #59, a reference to Belcher's uniform number.
"Murder is bad but honestly it was not premeditated," Taylor Gant said. "There is a difference between that and doing something out of the heat of the moment."
Gant said he "felt horrible" for Perkins and the baby and called them the real victims.
"I just don't think you need to completely throw away everything (Belcher) has done for the Chiefs," Taylor Gant said.
Kansas City Mayor Sylvester James likened the tragedy to "your worst nightmare."
"Its unfathomable," James told reporters. "It's something that you would love to wash away from your mind but you can't do it. There is nothing like it. Think about your worst nightmare and multiply by five."