Ventura County sheriff's investigators said that Gil and members of his Camarillo gang crashed the party.
"Witnesses said tension had been building, several fights broke out and unprovoked, Isaac Gil, stabbed Andrew," said sheriff's Capt. Rick Barrios.
Investigators said the suspect's gang ties made it tough to track him down.
Singler's parents had been waiting for this moment. They checked their e-mails daily for any developments in the investigation of their son's murder.
"It's been a long process," said Singler's father, Chuck. "We realize it's just one step, but at least it's closer."
Even though detectives early on believed Gil was their prime suspect, witnesses were reluctant to help because he is a gang member, Barrios said.
The young victim's friends and family say the man's arrest has given them some closure.
Gil's bail was set at $500,000.
Singler was two weeks shy of his 19th birthday when he was killed.