The New Jersey man who allegedly beat and stabbed his younger brother to death in a ritzy Princeton apartment posted a creepy poem to social media that included lines about “knives sharpening” and “blood oozing out of his eyes” several months before the killing.

Matthew Hertgen’s mugshot, released Tuesday, showed the hairy-faced murder suspect with a thousand-yard stare painted on his face after being accused of fratricide — in this case, killing 26-year-old Joseph Hertgen on Saturday night.

In September, the 31-year-old accused murderer wrote strange verses on his Facebook page that could indicate his fragile state of mind.

“What have you created?/ Why have you created it?/ Who are you trying to strangle?” he wrote. “And what god are you serving?/ I can see the knives sharpening/ I can hear the arrows whizzing/ I can feel my heart beating/ But can he?”

“Someone sits alone in that room/ That room where the walls shake,” the poem continued. “He still has a pulse/ Blood still flows through his veins/ But something is wrapped around him/ Squeezing him/ Choking him/ Suffocating him.”

“Tightly wound around his head/ Fastened deep in his throat/ Blood oozes out of his eyes,” he continued. “His ears are sparking/ His face vibrates/ He convulses, and he doesn’t stop/ He’s lost/ He’s asleep/ He’s dead.”

Matthew Hertgen has been accused of using a knife and a golf club to slash and beat Joseph to death at about 11:15 p.m. on Saturday night. 

He also allegedly killed the family cat — just a day after posting an odd Facebook selfie in which he laid on the carpeted floor next to an $8 cat toy, his bearded face displaying the same blank expression as his mugshot.

Cops went to the four-story Michelle Mews apartment complex off Witherspoon Street after Hertgen called 911 to report a fire and dead body in the apartment, the Mercer County Prosecutor’s Office said in a statement.

When officers arrived, they found Joseph’s bloody corpse and arrested his sibling.

Both brothers were high school and college soccer stars — Matthew at elite Wesleyan University and Joseph at the University of Michigan. The murder took place at the family’s apartment in a luxury complex, where units often go for $2 million, near the campus of Ivy League Princeton University. 

“The complaint alleges that Matthew purposely or knowingly engaged in conduct that led to the death of his younger brother and caused the death of a cat that was located within the residence,” the prosecutor’s statement said.

Hertgen has been charged with murder for the horrific slaying, and could face life in prison if convicted.

If convicted, he faces up to 30 years to life in prison.

After graduating from Michigan’s business school, Joseph worked as an analyst with Red Bank, NJ-based asset management firm Locust Point Capital, the company website said.

His brother, meanwhile, was arrested for drunk driving in South Jersey in February 2017, and lost his license for three months.

But other than that, he had not crossed paths with the law before the alleged killing.