In a stunning twist in the Brooklyn “one-punch killing” case, police are looking for a second suspect — who could have thrown the blow that led to Jose Zambrano Rodriguez’s death.

New surveillance video obtained by police shows a second suspect slugging Rodriguez in the back of the head before he hit the pavement and shattered his skull, sources familiar with the investigation told The Post.

A witness initially fingered alleged Latin Kings gang member Joshua Hernandez in the case. He is charged with second-degree felony assault, police said.

But video shows Hernandez, 25, was among a group of three who confronted the 26-year-old video game developer Nov. 17 around 4:30 a.m. on a Williamsburg sidewalk.

They claimed to be in search of a cigarette — but sources say they were looking for a fight.

Rodriguez stood his ground as Hernandez and the at-large suspect, dressed in all black, threw “probably four punches,” one source said of the video, then “one of the guys took a cheap shot, and he fell.

“It was like a frat party. Like [guys sparring] outside a bar,” the source said.

Hernandez was arrested later that morning — 72 hours before Rodriguez died in Bellevue Hospital — and released on $20,000 bail.

Police have since flagged the second suspect for arrest, a law enforcement source said, noting the accomplice could face similar assault charges.

“It doesn’t matter who delivered the last punch,” the law enforcement source said. “They were both involved, and the assault-2 charges refer to the injuries sustained regardless. It’s not about the death.”

The source was referring to the legal loophole in “one-punch killing” cases in which a person dies after a punch but their attackers avoid a murder or manslaughter charge because it cannot be proven they intended to kill their victim.

“The tragic outcome doesn’t necessarily correlate with the state of mind of the individual who committed the offense,” said former Manhattan prosecutor and criminal defense attorney Jeremy Saland. “You can’t ignore the catastrophic result of someone passing away . . . but at the same time, there is a difference between intentionally taking a life and not.”

Hernandez — who has multiple prior violent arrests — was initially charged with misdemeanor assault in the case, but the charges were upgraded to second-degree assault.

“It’s like two one-punch killers,” the law enforcement source said. “They were acting in concert, so they’re both equally responsible.”

Rodriguez’s family has decried the assault charges in the homicide case — and says they won’t be satisfied until his attackers are charged with manslaughter.