Two girls were throwing a graduation party when a group of five uninvited guests showed up.
Police they shot and killed a 21-year-old man.
A 15-year-old boy was also shot in the head but is expected to survive.
Police say he wasn't the intended target.
"The guy just took out a gun and started shooting up in the air and shot towards where we were at and i didn't see anything else," said Maria Ogara, who was at the party. "Everything went blank cause i thought they shot me."
The second graduation party was early Saturday morning at a home in the unincorporated community of home acres near Moorpark.
Police said Andrew Singler, 19, was stabbed to death after a fight broke out.
Officers don't know what started the fight and no arrests have been made.