(CNN) The suspect in a shooting that left three people dead in Washington state killed himself hours later after he borrowed a stranger's phone, called his mom and made "incriminating statements, including, 'I killed those people,'" the Yakima police chief said Tuesday.
The suspect had "a large amount of ammunition" and a semi-automatic handgun at the scene where officers found him, Chief Matt Murray said in a Tuesday evening news conference, adding the motive is under investigation.
The attack early Tuesday at a convenience store appeared "very much random," the chief said, and is part of a spate of gun violence that left 24 people dead across three US states starting late Saturday, including three mass shootings in California in just 44 hours.
The "presumed homicide suspect" in Yakima had been identified as Jarid Haddock, 21, of Yakima County, by police on Facebook.
The suspect had pulled into an ARCO/ampm gas station around 3:30 a.m. and "tried to get into the lobby" but found the doors locked, the chief told CNN on Tuesday.
"He then walked across the street to the Circle K," Murray said. "As he's walking into the store, he pulls out his gun and there are two people getting food and he shoots them."
Both died, he said.
"There was no interaction between him and people," the chief said. "They were just sitting there getting food and got surprised by this person who came in and ... literally as he was opening the door, he started shooting these people."
The suspect then walked out of the store and shot another person, who also died, before crossing the street to the ARCO/ampm gas station, shooting into a car and driving off, Murray said.
Justin Bumbalogh heard the shots while half-asleep next door to the Circle K at his job at Elite Towing and Recovery, he said.
Around nine shots rang out, with a distinct gap between two series, he said, before police quickly responded.
Police later Tuesday surrounded a house where they thought -- but never confirmed -- the suspect had holed up, Murray said, adding the suspect's family had cooperated with police throughout the day.
"He was out in the community," the chief said. "So, the threat was never really gone."
Later, a woman near a Target store in Yakima lent the suspect -- an apparent stranger -- her phone and heard him talk with his mother and say he would kill himself, the chief said.
She managed to get the phone back and call 911, he said.
"I listened to that call. It's pretty harrowing," Murray said. "And I have to really thank her again because she was very courageous in getting us there."
Officers responded within minutes to find the suspect had fatally shot himself, Murray said.
"I can say with pretty good confidence that we believe that this is the person who was involved" in the Circle K attack, Murray said, noting officials still must formally identify him.
The FBI's Seattle Field Office was aware of the shooting and had been in contact with Yakima Police, agency spokesperson Steve Bernd told CNN.