The body was found early Monday on Iona Island, part of Bear Mountain State Parkway, which is patrolled by New York State Park Police.
At about 8:30 a.m., a recreational boater aboard a sailboat spotted Kim's body in the river just south of the Bear Mountain Bridge, near the Rockland County shoreline, authorities said.
Hours later, the medical examiner's office identified the body as 63-year-old Sang Ho Kim, the man believed responsible for the deadly workplace shooting in Garden City last week.
Meanwhile, family and friends gathered in Queens Monday to say goodbye to one of the victims, 25-year old Zachariah Yong Jae Shin. A wake was held Sunday night in Flushing to remember Shin, who worked at the light fixture firm SavEnergy.
The owner of the firm, 68-year-old John Choi, was shot in the head, but survived.
Authorities say Kim entered SavEnergy near the Roosevelt Field Mall in Garden City around 10 a.m. Wednesday and opened fire.
Kim was reported to have fled in the direction of the nearby Roosevelt Field mall after the shooting, touching off lockdowns of businesses in and near the mall and of nearby schools. Some customers later said they had fleeting concerns about a copycat terrorist attack like the one that took place at a mall in Kenya over the weekend.
Kim's abandoned SUV was found inside Sandy Beach Park in Cold Spring, Putnam County in a heavily wooded area that is not far from the Hudson River and close to a commuter railroad station.
Police on Long Island said the shooting appeared to have stemmed from a business dispute between Kim and Savenergy officials.
"There was some disgruntlement between him and the company he was attacking," Nassau County Police Chief Steven Skrynecki said Wednesday. "We have nothing to suggest that this individual is on a random, shooting rampage."