Colorado Springs Mayor John Suthers said Monday that the mass shooting over the weekend at a birthday party inside a mobile home appeared to be the result of domestic violence, a report said.

The Colorado Springs Gazette reported that there are still many unknowns about the shooting that left seven dead, including the gunman who was believed to be the boyfriend of one of the female victims.

The paper reported that Suthers told KKTV, its news partner, that it seems that the shooting was not a "domestic terrorism incident."

"It appears to be domestic violence…that there was a relationship here that the perpetrator was involved in, and unfortunately, we had a lot of bystanders who got killed," he said.

Police say the suspect "drove to the residence, walked inside and began shooting people at the party before taking his own life," adding that "friends, family, and children were gathered inside the trailer to celebrate when the shooting occurred." 

Suthers told KKTV that the only time that there were so many victims in a killing in the city occurred during an ax murder in 1911.

Police say the names of the suspect and victims will be released after a coroner has confirmed their identities and cause of death. There were children at the birthday party who were not targeted.

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The attack was Colorado’s worst mass shooting since a gunman killed 10 people at a Boulder supermarket March 22. 

The Associated Press contributed to this report