A Bronx man was held without bail Sunday after allegedly killing a stranger who appeared to simply show up at the wrong place at the wrong time, as new details emerged in the grisly slaying.

Suspect Jose Ortiz, 65, is accused of fatally stabbing Tyrone Quick, 45, in the heart at a University Avenue apartment in Highbridge, where the victim was visiting a friend, Vanessa Guzman, cops and new court documents say.

Guzman had been trying to hide from Ortiz, who was allegedly threatening to kill neighbors for no apparent reason. Police say Ortiz slashed Guzman in the chest. Then after Quick arrived, Ortiz stabbed him three times, “piercing his heart and causing his death,” according to the suspect’s criminal complaint Sunday. 

The defendant was led into Bronx court Sunday afternoon with his hands cuffed behind his back and wearing a blue golf shirt, dark gray khaki slacks and black sneakers.

“Mr. Ortiz stands accused of murder and attempted murder, and we request remand,” Assistant District Attorney Joshua Fetterman said.

Judge Margaret Martin remanded Ortiz at least until till his next court hearing. 

Ortiz was charged with murder, attempted murder, manslaughter, attempted manslaughter, assault and criminal possession of a weapon. 

One of Guzman’s neighbors, Justina Cruz, has told The Post she was tending to her friend’s wound in her apartment when Quick was stabbed.

“I had no idea that Tyrone was right in front of my f–king door fighting for his life. I didn’t know or I would have helped him, I would have helped him. I didn’t know,” she sobbed. calling the attack “your worst nightmare.”

After Quick — who visited Guzman every day —  was stabbed, he got on the building’s elevator, took it to a higher floor and collapsed, she said. 

Guzman was taken to the hospital after the attack for her chest injury. 

The Bronx building is designated for previously homeless residents, low-income New Yorkers and individuals with mental-health issues.