The longtime criminal accused of killing eight people in suburban Chicago was related to most of the victims, according to a police chief who called it “probably the worst crime” he’s investigated in nearly 30 years.

Investigators believe Romeo Nance, 23, began his shooting spree at two homes across the street from each other in Joliet on Saturday afternoon — even though their bodies were not found until Monday morning.

Inside one they found the bodies of his relatives Alexandria Nance, 20, Christine Esters, 38, and Joshua Nance, 31, as well as two unidentified girls, ages 14 and 16.

Across the street, they found the bodies of Tameka Nance, 47, and William Esters II, 35.

It was not immediately clear how they were related to Nance, who was accused of later shooting a 42-year-old man in the leg before gunning down his final victim, Toyosi Bakare, 28, who is thought to be a stranger out shopping.

“We’re still sorting through that,” Joliet Police Chief Bill Evans said of the exact relationships.

His officers are even more baffled as to the motive for the mass shooting by Nance, who eventually shot himself dead after being confronted by law enforcement officials in Texas.

“We can’t get inside his head,” Evans said.

“We just don’t have any clue as to why he did what he did,” said the nearly 30-year veteran, calling it “probably the worst crime I’ve ever been associated with.”

Nance’s two attacks after shooting up his relatives’ homes appear “more random in nature” with no known “nexus” to the initial carnage, the chief said.

First, surveillance footage showed him in his red Toyota Camry passing a 42-year-old man walking with groceries.

Nance was seen talking to the man before driving to the end of the block, making a U-turn — and opening fire.

“It was nine gunshots,” neighbor Curtis Ellis told CBS News. “That’s a whole clip that he was trying to load in this guy — and lucky that he just didn’t hit a vital organ.”

Nance was seen talking to the man before driving to the end of the block, making a U-turn — and opening fire.

The 42-year-old man was hit in the leg and survived, officials said.

About 10 minutes later, Nance shot and killed Bakare, a Nigerian immigrant, at the final victim’s apartment complex.

Bakare was found bleeding on the ground, and was rushed to a local hospital, where he was pronounced dead.

Bakare was simply out to buy cigarettes at a local gas station when he was gunned down, cops said.

Nance was eventually tracked by US Marshals to Texas, where he shot and killed himself Monday night.

Investigators believe he stopped at a mall and stole license plates for his vehicle to throw law enforcement off his trail before he was eventually found, Evans said.

He noted that Nance had an extensive criminal history.