The deli worker accused of fatally stabbing his Harlem ex-girlfriend in a jealous rage early Monday was coolly going about his business at his Bronx job just hours before the slaying, haunting new video shows.

Luis Marquez, 41, is facing murder charges for allegedly knifing Carmen Lopez up to 50 times when he ambushed her inside her West 129th Street apartment building around 4 a.m. after lying in wait for two hours.

But leading up to the frenzied attack, footage obtained by The Post showed the suspect milling around his job at RC Meat Market in his “usual” demeanor before punching out around 7 p.m. on Sunday.

Suspected killer Luis Marquez, 41, is facing murder charges for allegedly knifing Carmen Lopez dozens of times. Stephen Yang for NY Post

The video showed him wearing a black apron and ball cap as he’s cleaning up equipment behind the counter along with another worker.

As he left, he even told his boss he’d see him the next day.

“We closed down and I said ‘bye, bye.’ He said, ‘I’m going this way.” I said, ‘take care of yourself,’ and he said, ‘okay, I’ll see you on Monday,’” owner Ramon Cedano told The Post.

When Cedano found out Marquez was implicated in the murder, he was stunned and even checked surveillance video to see if there was anything off about his employee.

“I looked at my camera to see if I see something but nothing, nothing,” he said.

Lopez was brutally murdered inside her West 129th Street apartment building around 4 a.m.

“He came to work like usual. He punched in, he was doing what he had to do and being him – calm, quiet, closed [off] as usual.”

Following the early morning ambush, he allegedly rambled to his family that he killed Lopez, a 47-year-old mother of four, according to sources.

He was then taken for a psychiatric observation at a local hospital, where he was first taken into custody by police, authorities said.

Footage obtained by The Post showed Marquez working at his job at RC Meat Market, wearing a black apron and hat, cleaning up before telling his boss he would see him tomorrow. Obtained by the NY Post

Marquez and Lopez dated on and off for the past several years, with friends claiming Marquez was obsessively jealous and angry she didn’t give him more attention.

Start your day with all you need to know

Morning Report delivers the latest news, videos, photos and more.

Thanks for signing up!

The pair were not dating at the time of the slaying.  

Lopez’s badly injured body was found by a building porter. She was rushed to the hospital where she was pronounced dead.