The Sheriff's Department believes the 14-year-old suspect is affiliated with a local street gang. He was arrested at his home in Mira Monte at about 7 p.m. Sunday.
Authorities also arrested 21-year-old Gabriel Arellano of Oak View in connection with the murder, although Arellano is not suspected of stabbing Scarminach.
Arellano remains in custody on $110,000 bail. He was booked on suspicion of felony participation in a criminal street gang.
Ventura County Sheriff's investigators found evidence of alcohol and marijuana at the party. They say the party was not supervised.
The Ventura County Star contributed to this report.
MORE LOCAL HEADLINES FROM VENTURA COUNTY
SEND TIP || REPORT TYPO || TWEET @abc7 || WIDGET