Lopez-Fregoso was taken to the Hemet Police Station and was interviewed by detectives for several hours. Lopez was released pending further investigation.
Police are still looking for Jose Campos, 17, in connection with the killing of Adrian Rios. Campos's girlfriend, 17-year-old Felicia Sharp is also being sought.
Campos's stepfather and mother, Jose and Maria Seym, were arrested late Thursday on suspicion of being accessories to murder, said Hemet Police Capt. Tony Margis.
Charred human remains were found in a shallow grave in the backyard of their home on the 1400 block of Bluejay Way on Nov. 18. Police also found a machete, butcher knives, a bullet casing, burnt clothing and an empty gas canister at the home.
Police said they believe the charred remains are those of Rios, who was last seen at the home, although the remains have not yet been positively identified. Police are awaiting the results of DNA testing on some of the remains, including a severed human foot, which could take several weeks.
Detectives said Rios was shot to death and set on fire in an attempt to conceal the crime. They said Rios is believed to have been murdered with a total of six people present during or just after the crime.
"We do believe that he was murdered and he was murdered prior to being placed in the fire pit and burned. There was a number of people at the residence, either at the time of the murder or immediately thereafter. There were more than six people that arrived at that location," said Hemet Police Chief Richard Dana.
Hemet Police Capt. Tony Margis said the Seyms are not believed to have been at the home when Rios was killed.
"Right now, the parents are being held as accessories, so their role would be regarding their activities after the homicide," Margis said.
Campos, Rios and Sharpe were all initially reported missing last month, having last been seen at the home Nov. 15. Neighbors said there was a bonfire with a foul stench at the home that night.
"It was a horrible, very bad smell," said neighbor Matthew Miller.
Police said they believe Adrian Rios was murdered the night of Nov. 15 or early Nov. 16. Police following up on a missing-persons report filed by Rios's mother searched the Bluejay Way home and found human remains in the backyard.
Police have not determined a motive or recovered a murder weapon. However, they are looking into whether the murder was gang-related.
Shortly after the remains were discovered, Sharpe walked into a Hemet police station with her mother, where she was questioned and released. She has since disappeared again.
Police have not commented on what Sharpe may have told them about the boys.
Campos had lived in the home for the past two months with his parents, but neighbors said the home had been vacant for about a week before the night of the bonfire.
Police said the two suspects are armed and dangerous. If you have any information on the suspects' whereabouts, you're asked to call Hemet Police at (951) 634-3046.