The laid-off designer who executed a former co-worker outside the Empire State Building spent two years blaming his victim for his financial woes — but he finally snapped when he learned he was being evicted from his Upper East Side apartment, The Post has learned.

“This was the final straw that pushed him over the edge,” a police source said yesterday. “He was blaming the victim for being out of work, having no money and now having no apartment.”

Shooter Jeffrey Johnson — who served in the Coast Guard as a petty officer second class in the 1970s — brooded over his dismissal from Hazan Import at 10 W. 33rd St., where he worked for six years.

He was laid off simply because “business was bad,” a Hazan employee said.

But for Johnson, the blame rested on salesman Steven Ercolino, who the shooter thought was not doing enough to push the products he designed, a source said.

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Even before his layoff, Johnson and Ercolino were already on poor terms.

“Johnson filed a complaint against Ercolino saying he had a confrontation with him in the lobby of the building,” Police Commissioner Ray Kelly said yesterday.

“Ercolino filed a complaint saying he was threatened by Johnson and he possibly threatened to kill him.”

His breaking point came when his landlord threatened the man with eviction.

Johnson was no longer able to make rent on the one-bedroom co-op he had rented on East 82nd Street for about four years and kept methodically clean, a police source said.

Johnson — a bird-watcher who just last Wednesday blogged about his hobby in Central Park — blamed that on Ercolino, and on Friday exacted his revenge.

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Wearing a full suit, Johnson lay in wait behind a truck outside the 33rd Street building until Ercolino arrived around 9 a.m.

He shot his defenseless victim in the head and then pumped another four bullets into his body.

The killer then calmly turned the corner to Fifth Avenue, where he drew his gun on a pair of NYPD cops on anti-terror patrol.

The officers fired 16 times, killing him and wounding nine pedestrians with bullets and ricochet fragments.

The three victims directly struck remained hospitalized yesterday, Kelly said.

Ercolino’s longtime girlfriend, Ivette Rivera, bared her grief on Facebook yesterday morning.

“My life will never be the same without my baby, my protector, my best friend, my everything,” she wrote.

“It will be hard to face every day without him by my side. No words can describe my pain.”

“I don’t know how to live without him,” she added. “I need him so much.”

The couple had been together for years and shared an apartment in New Jersey.

They were “very happy together,” a pal said.

Just Monday, they went to a Mets game at Citi Field. Before that, on Aug. 11, she wrote on Facebook about going to Atlantic City for a Journey concert “with my boy” and boasted of having “hit a jackpot right before.”

“They used to go to work together every day in the morning, take the shuttle into the city,” said Danny Garcia, 40, the doorman at the couple’s building. “They were very nice people.”

“He was just a normal guy — took care of himself, went to the gym everyday,” Garcia added. “Everybody liked them here.”

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Meanwhile, Ercolino’s distraught family gathered in upstate Warwick yesterday afternoon as they tried to make sense of the tragedy.

“He was the light of our lives,” said the victim’s brother, Paul Ercolino. “He was the one that was the adventurous one. He loved life. He had a zest for life.”

“He loved his Jets, he loved his Mets,” Paul Ercolino added. “He loved his nieces and nephews — they were the world to him.”

“I’m going to miss him terribly.”

Ivette is “just distraught,” Paul Ercolino said. “She’s absolutely distraught. He was her rock.”

Neighbors described Ercolino as a helpful man who always had a smile to spare.

“He was just one of the most generally nice people I’ve ever met,” said Danny J., 29, who used to work out with Ercolino. “If you needed anything, he would offer any help that he could.”

Back at the Empire State Building, workers tried to return to their normal routines.

“Coming in to work today was tough, too fresh,” said Miguel Castro, 26, who works for NY Skyride. “Every time I hear a loud sound I get scared, my heart goes fast. It’s terrible.”

About six cops were stationed outside the building, instead of the usual two, a worker said.

“Tourists are coming by and asking, ‘Is this where the guy was shot?’ ” Castro said. “It’s crazy.”

One tourist, Bruno Bombino, 35, originally visited the skyscraper on Friday — but never made it in during the chaos of the shooting.

“It was pandemonium,” said Bombino, visiting from Toronto with his wife, Felicia. “I heard, ‘Pop, pop, pop!’ ”

“It hadn’t sunk in yet, but you think about it after and it’s pretty freaky,” he added. “It could have been us who got shot.”

Additional reporting by Rebecca Harshbarger, Kate Kowsh and Kevin Fasick