The body of Madyson "Maddy" Middleton, who was reported missing Sunday evening, was found Monday in a recycling bin at the Santa Cruz apartment complex where she and the teen lived, Santa Cruz police Chief Kevin Vogel said.
The boy, a 15-year-old acquaintance of Madyson, was arrested on suspicion of murder, Vogel said.
"We have evidence that ties our suspect to Maddy, but with respect to what that evidence actually is, I'm going to hold back on that information," the chief told reporters.
The girl trusted the teenage boy, Vogel said.
"They were alone in the apartment," the chief told reporters. "She willingly accompanied him up to the apartment."
"She was 8 years old. She had a reasonable amount of trust in him," Vogel said. "They were acquaintances. I don't know to what degree they were friends."
The boy was arrested immediately after police found the girl's body because the boy "was in the general proximity" of the recycling bin and may have been watching police search it, Vogel said.
Vogel declined to say how she was killed. An autopsy has yet to be performed, Vogel said.
Authorities have interviewed the boy, but Vogel declined to reveal what the boy said. The chief also declined to state a motive.
"Our hopes and prayers were that we were going to find Maddy alive," the chief said.
But the body was found after police shifted from a rescue to a recovery operation and conducted a more intensive search, the chief said.
"The body was located within the recycle bin in a way that if you just merely opened the top of the bin, you would have not seen the body," the chief said. "She was not readily visible."
Investigators believe that the girl was killed upstairs and then her body was later dumped in the bin, the police chief said.
"It's my belief that she was killed even before we got the phone call Sunday" at about 6 p.m. when she was reported missing, Vogel said.
Witnesses last saw the 4-feet-tall, 48-pound girl at 5 p.m. Sunday while she was riding a white Razor scooter with her long hair pulled to the side in a braid, police said.
Police are still investigating the killing, and the chief suggested that investigators will re-interview the boy's family as well as other people.