A California man was busted for the mass overdose in Pittsburgh that killed three people and put four others in the hospital  over the weekend, according to police.

Peter Rene Sanchez Montalvo, nicknamed “Carlos,” was arrested around 3 a.m. Monday for allegedly providing the victims with a white powder they believed to be cocaine — but instead contained fentanyl — at an “after-party” at a South Side apartment, Pittsburgh police said.

The victims all wore orange wristbands that were distributed to patrons of the Insomnia Discotec in Brookline on Saturday night — where investigators say Montalvo was also present, police said.

“At some point in the evening, Sanchez Montalvo left Insomnia and went to the South Side apartment, where he had been staying,” authorities said in a statement.

“Several other individuals who were at Insomnia, including members of the band that played at the bar on Saturday night, joined him for what was described as an ‘after-party,” the statement said.

“Sanchez-Montalvo distributed a white powdered substance, believed to be cocaine, to those in attendance. Shortly after, multiple people became seriously ill. Three of them died at the scene.”

The mysterious illnesses initially baffled cops. Police initially received a call at 2 a.m. Sunday for a man found unconscious on a city street. The man was rushed to a nearby hospital.

Not long after another man was found unconscious in the elevator of The City Apartments on Tunnel Boulevard and was pronounced dead at the scene.

Then, just before dawn, five more victims — two dead and three unconscious — were found inside an apartment in the building.

The Daily Beast identified the dead as Rubiel Clemente-Martinez, 32, Joel Pecina, 32, and Josue Soberal Serrano, 38. The condition of the surviving victims ranged from serious to critical.

Montalvo could face up to life in prison and a $1 million fine if convicted.