Fahim Saleh, 33, was followed into his luxury Manhattan condo by a man dressed all in black, the official said.
The killer, dressed entirely in black and wearing a black mask, followed the young technology entrepreneur from the elevator of his luxury condo building into his apartment.
Then he fired a single bullet that hit the entrepreneur, Fahim Saleh, in the back of the head.
Sometime after, the assailant decapitated Saleh and dismembered his body with an electric saw.
That was the chilling account that a law enforcement official briefed on the investigation gave Wednesday as investigators continued scrutinising evidence in the shocking killing of Saleh, 33, whose body parts were found Tuesday in plastic garbage bags in his apartment on Manhattan's Lower East Side.
On Wednesday, the police continued their investigation at the building and inside Saleh's apartment, a seventh-story unit that he bought last year for US$2.25 million ($3.4 million), public records show, and for which he expressed his affection on Instagram.
The investigation included a review of surveillance video from Saleh's apartment building and an interview with his sister.
Investigators believe the killer's work dismembering the body was interrupted when the victim's sister entered the apartment to check on him after not hearing from him for a day, another law enforcement official said.
Detectives think that the assailant fled through the apartment's back door and into the building's stairwell when she arrived, the official said.
A Police Department spokesman said he could not comment on how the killer entered the building. The property's management company said that the building did not have a doorman but had extensive security in place.
The management company, in a statement, said Saleh was an active member of the condominium board.
"The unit owners, residents, board and management are all quite upset," the statement said.
On Tuesday, a law enforcement official said that the electric saw was still plugged into an electrical outlet when the police arrived, and the killer had left some cleaning supplies behind. It appeared that some effort had been made to clean up the evidence.
The official who spoke Wednesday said that the killing "looks like a professional job," referring to it as a "hit." A Police Department spokesman said he could not comment on a possible motive or whether any suspects had been identified.
On Tuesday night and Wednesday morning, detectives were scouring the neighbourhood for surveillance video from outside local stores, residential and commercial buildings and area traffic cameras to see if cameras had captured the killer coming or going or waiting for his prey, several law enforcement officials said.
The grisly death has attracted international attention given Saleh's global connections. The son of Bangladeshi immigrants, Saleh founded ride-hailing companies in Bangladesh and Nigeria as well as a venture-capital fund based in Manhattan that invested largely in companies in the developing world.
On Wednesday, Bangladesh's minister for information and communication technology, Zunaid Ahmed Palak, expressed his condolences and said on Twitter that Saleh's death was a great loss for the country.
Saleh's family has declined to speak to the press.
Sumeet Rametra, who met Saleh in college and has been in close communication with his family since his death, described his friend as someone who indulged in kind gestures, like buying his parents a home and a Tesla.
On one recent occasion, Saleh asked Rametra to join him for a game of tennis, but Rametra said he didn't have a racket, he recalled.
"He was like, 'I already got you one, let's go,' " Rametra said, crying. "I never got to play with him."
Rametra, 31, also lauded Saleh's business acumen, saying that his friend was a visionary who was always looking to his next idea.
"He was a machine, dude, he never stopped," Rametra said. "He was always trying to make money."
Saleh grew up near Poughkeepsie, New York, according to public records. As a teenager, he learned to code and began to develop websites, his friends said. He graduated from Bentley University, a small college in Waltham, Massachusetts, in 2009 with a degree in computer information systems, according to his LinkedIn profile.
On social media, in interviews and blog posts, Saleh depicted himself as an entrepreneur driven by passion.
"Entrepreneurs are the ones that really change countries, that really change cities," Saleh said in a YouTube video in February. "They're the ones that bring the vision."
After college, Saleh turned his love for practical jokes into a prank-calling app named PrankDial, which allowed users to buy prerecorded calls to send to friends.
Writing years later about the business, Saleh said that it eventually generated millions and led him to realise that he could keep turning his passions — in this case, for practical jokes — into big bucks.
"If you go into a project entirely focused on making money, you're going to be disappointed," he wrote in a post on Medium.
Still, PrankDial had its stumbles. On his LinkedIn profile, Saleh boasted that while his company had millions of downloads, it also drew more than 100 subpoenas.
At the time of Saleh's death, PrankDial and its owners faced an active lawsuit from a New Jersey jail worker who was convicted in 2015 of using the site to illegally wiretap his co-workers.
After PrankDial, Saleh turned his attention to Bangladesh, where he co-founded the ride-sharing company Pathao in 2015. The business, which Saleh left in 2018, started as a bike-sharing company but now offers transportation, delivery and business logistics.
"Fahim believed in the potential for technology to transform lives in Bangladesh and beyond," Pathao said in a statement.
Fueled by his success in Bangladesh, Saleh tried to launch a similar venture in Nigeria. That company, Gokada, began operating as a motorcycle ride-hailing company in Lagos, Nigeria's most populous city, in 2018.
Motorcycle taxis, called okada in Nigeria, have long been popular in Lagos and many other African cities as a way to circumvent traffic jams. Gokada raised $5.3 million in venture capital in June 2019, according to the website TechCrunch.
But Saleh's business hit a major stumbling block in February, when state officials banned motorcycle taxis from operating in major commercial and residential parts of Lagos.
Gokada was forced to halt its ride-hailing business. In a video discussing the ban, Saleh, the company's chief executive, appeared crestfallen.
"This has definitely been a blow," Saleh said in the video, which he posted to YouTube and social media platforms on February 2 and titled "Gokada is not okada."
Saleh was forced to lay off workers, friends said. But he tried to rebound, saying he still believed that Nigeria had enormous economic potential and that he could provide jobs to young Nigerians.
In February, Gokada pivoted quickly to a food and package delivery service. After the change, Saleh sounded an optimistic note.
In April, as the pandemic upended New York and Nigeria alike, he noted on Twitter that his company was well positioned to adapt to the economic shift.
"Now it seems like we had a two-month head start in one of the few thriving business sectors," he said.
The law enforcement official said that investigators were exploring on Wednesday whether Saleh's killing might be related to his business, noting the indications that his company had been hurting.
Even as his startup encountered setbacks, Saleh had remained both hopeful and persistent.
"Have a very good feeling about 2020," he said on Twitter on June 2.
Written by: Michael Gold, William K. Rashbaum and Daniel E. Slotnik
Photographs by: John Taggart
© 2020 THE NEW YORK TIMES