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 Mr. Saleh’s seventh-floor unit, the assailant fired a Taser into Mr. Saleh’s back, immobilizing him, at about 1:44 p.m. on Monday, according to a criminal complaint. He then stabbed Mr. Saleh to death, wounding him multiple times in his neck and torso.
The next morning, Mr. Haspil used a credit card to hire a car to go to a Home Depot, on West 23rd Street in Manhattan, and to buy an electric saw and cleaning supplies, the fourth official said. The criminal complaint said he was captured on video by a store camera buying the goods at 9:30 a.m.
Later that day, dressed in a gray hooded sweatshirt, the assailant returned to Mr. Saleh’s apartment to dismember the body and clean up the crime scene.
Security video from inside Mr. 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, Mr. 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, Mr. Haspil graduated from Central High School in Valley Stream, N.Y., 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.