NEW YORK (NYTIMES) - When a young tech entrepreneur with a history of doing business in Nigeria and Bangladesh was found dismembered this week in his multimillion-dollar Manhattan condominium, the case at first seemed to have all the trappings of an international thriller.

Someone in a black suit, a mask and latex gloves had followed the victim, Fahim Saleh, into his apartment while carrying a duffel bag, a security video showed.

The person then subdued Saleh with a Taser, stabbed him to death and returned the next day to dismember him with an electric saw, police said.

One law enforcement official said it "looked like a professional job."

But instead of leading detectives toward Saleh's overseas business projects, the evidence quickly pointed to someone close to home, police said: his onetime personal assistant.

On Friday (July 17), the former assistant, Tyrese Devon Haspil, 21, was arrested and charged with murdering Saleh, 33.

Some investigators theorised that the suspect had tried to make the killing look like a professional assassination to divert attention from himself.

"Mr Haspil was Mr Saleh's executive assistant and handled his finances and personal matters," the chief of detectives, Rodney K. Harrison, said at a brief news conference Friday afternoon. "It is also believed that he owed the victim a significant amount of money."

According to three officials briefed on the matter, Saleh had discovered that Haspil had stolen roughly US$90,000 (S$125,088) from him.

Though Saleh, who friends said was a generous man, fired Haspil, he did not report the theft, the officials said. He even offered to arrange a way for his former employee to work off his debt in what amounted to a payment plan.

Haspil, a Long Island native who had recently attended Hofstra University, was arrested at 8:45am Friday in the lobby of a building at 172 Crosby St. in SoHo, where he had been staying in an apartment with a female friend, one official said.

New York detectives and federal agents from a US Marshals Service regional fugitive task force took him into custody.

"He tried to run," said the building's superintendent, who declined to give his name, explaining that he was not authorised to speak on behalf of the owner.

The superintendent added that Haspil had arrived at the Crosby Street apartment at some point Wednesday and that he was planning to leave Monday.

Saleh was discovered dead Tuesday, when his cousin went to check on him at his US$2.25 million condo in a luxury building on East Houston Street on the Lower East Side.

The cousin, officials said, was worried after not hearing from him for about a day.

When the cousin got to the apartment, police said, she discovered a horrifying scene: Saleh's head and limbs had been removed, and parts of his body had been placed in plastic bags designed for construction debris. An electric saw was plugged in nearby.

Investigators have concluded that Saleh had been killed the day before, according to a fourth official with knowledge of the inquiry.

A video shows the man police believe to be Haspil following Saleh into his building and then into an elevator, where they appear to engage in small talk, the officials said.

The suspect was dressed in a black three-piece suit and wore a black mask and latex gloves, the officials said. He was carrying a duffel bag.

As the two men left the elevator, which opened directly into Saleh's seventh-floor unit, the assailant fired a Taser into Saleh's back, immobilising him, law enforcement officials said.

He then stabbed Saleh to death, wounding him multiple times in his neck and torso.

After the attack, the suspect used a credit card to hire a car to go to a Home Depot, on West 23rd Street in Manhattan, and to buy cleaning supplies, the fourth official said.

The next day, dressed in a gray hooded sweatshirt, the assailant returned to Saleh's apartment to dismember the body and clean up the crime scene.

Security video from inside Saleh's elevator showed that the suspect used a portable vacuum cleaner, perhaps in an effort to remove residue that was left behind when the Taser was fired, the officials said.

But while the assailant was cutting up the body, Saleh's cousin buzzed the apartment from the building's lobby. Before she got upstairs, the attacker fled through a back door and down a stairwell, officials said.

Only four years ago, Haspil graduated from Central High School in Valley Stream, New York, where he won an award for website design, according to local news articles. In 2017, he entered Hofstra as a member of its class of 2021.

Detectives believe that he began working for Saleh when he was 16 and eventually started managing some of his finances as well as taking care of personal matters, like caring for his dog.

One official said Saleh paid him well enough that he was able to settle the debts of several members of his family.

Haspil had recently lived on Woodruff Avenue in Brooklyn, where Kate Hain, one of his neighbours, said that nothing about him suggested he was capable of homicide.

"He and his roommate seemed to keep to themselves and not cause any issues in the building," Hain said.

She added that Haspil had done "nothing unusual" in all the time he lived there.

Saleh was born in Saudi Arabia to Bangladeshi parents who eventually settled near Poughkeepsie, New York, a small city on the Hudson River. In a statement earlier this week, his family called his death an "unfathomable" shock.