Left, an undated photo of Kasandra Michelle Perkins, Jovan Belcher's...

Left, an undated photo of Kasandra Michelle Perkins, Jovan Belcher's dead girlfriend, with daughter Zoey Michelle Belcher. Right, Jovan Belcher of the Kansas City Chiefs watches from the sideline during his final game against the Denver Broncos at Arrowhead Stadium in Kansas City, Mo. (Nov. 25, 2012) Credit: Facebook, Getty Images

Tension between Kansas City Chiefs linebacker Jovan Belcher and girlfriend Kasandra Perkins -- whom police said he fatally shot before killing himself at Arrowhead Stadium -- escalated after the birth of their daughter three months ago, her family and friends said Sunday.

"It wasn't a healthy thing that was going on," Angela U. Perkins, 32, of Round Rock, Texas, said of the relationship between Belcher and the cousin she knew as "Kasi."

Belcher's family members, however, cautioned against speculating about the couple's relationship, saying the former West Babylon High School football star had never displayed any violent tendencies.

Belcher, 25, and Kasandra Perkins, 22, were "the only people who knew what went on in their relationship," Belcher's sister, Charmaine Shepherd, said outside their childhood home Sunday. "And both of them are gone."

The infant, Zoey Michelle Belcher, was unharmed on Saturday and is in the care of Belcher's mother, Cheryl Shepherd, 58, Kansas City Police said. Cheryl Shepherd, who police said witnessed her son shoot Kasandra Perkins "multiple times" Saturday morning in their Independence, Mo., home, was to return to Long Island with the baby, family members said, without specifying a time.

Cheryl Shepherd Sunday said her family was heartbroken over both deaths.

"Right now, we are grieving for Kasandra and Jovan," she said in a telephone interview. "We are in mourning."

Neither family had released funeral arrangements as of Sunday night.

Shock over the murder-suicide rippled from Kansas City, where both families gathered near the Jackson County medical examiner's office and the Chiefs played a day after the shootings, to West Babylon, where Belcher was a high school football and wrestling star.

Police Sunday did not release any new details about the investigation and did not offer a motive for the murder-suicide. Police said Saturday that the couple had been fighting after Kasandra Perkins attended a concert with friends.

After shooting his girlfriend, Belcher drove the few miles to the Chiefs' practice facility and spoke with general manager Scott Pioli, coach Romeo Crennel and defensive coordinator Gary Gibbs, thanking them for the opportunity to play, before shooting himself in front of them, police said.

Eric Oakes, who said he was a cousin, said Belcher didn't experience any head trauma from football recently and wasn't on any medication. Oakes, 20, called Belcher "more than a cousin. He was a father figure. He's the reason I started playing football."

Chiefs owner Clark Hunt said Sunday that Belcher, a starter who was in his fourth season with the team, had no unusual physical issues before Saturday, including concussions.

"We lost two members of the Chiefs family," Hunt said, noting that Kasandra Perkins had done work for the team's women's organization.

At Arrowhead Stadium, where the Chiefs defeated the Carolina Panthers, a moment of silence was held for all victims of domestic violence, with no specific mention of names. Players later announced plans to set up a fund for Zoey.

Kasandra Perkins had gone out Friday night with girlfriends to a Trey Songz concert "to take a break," said friend Lynell Diggs.

"He [Belcher] didn't want her going out with the baby at home," said Diggs, who was among the group of friends at the concert.

Cousin Angela Perkins, who said she spent time at the couple's home both before and after their daughter was born, said the stress of having a baby just before the season and Belcher's constant time away from home for practices and road games "really put a strain" on the relationship.

"There was just a lot going on. She was stressed. He was stressed," Perkins said. "It just started to go bad, but they had the child, and they were trying to make it work."

Lauren Hall, 25, who said she was also at the Trey Songz concert, recalled Perkins as a "happy new mom" who had a busy social life after moving from Dallas three years ago.

"She strolled the baby around the neighborhood," Hall said. "She was really looking forward to raising her here and becoming a teacher" in Kansas City.

In West Babylon, a makeshift memorial with flowers, balloons, posters and Chiefs jerseys had been set up outside Belcher's mother's home. A helmet from his days as a football player at the University of Maine and a West Babylon High School varsity jacket had also been added.

By Sunday afternoon, more than 20 friends, former teammates and family members had visited the Matthews Avenue home.

"It's hard to figure out," said Emanual Logan, who lives next door and recalled how Belcher hosted a block party for children in the neighborhood this past summer.

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