On Sunday, the train was about half full, with about 150 people aboard, when it ran off the rails around 7:20 a.m. while rounding a bend where the Harlem and Hudson rivers meet. The lead car landed inches from the water. In addition to the four people killed, more than 60 were injured.
Many victims had been released from hospitals by Monday afternoon.
Seven were still in an intensive-care unit at St. Barnabas Hospital, some with spinal injuries, emergency department director Dr. David Listman said. And two patients were reported in critical condition at NewYork-Presbyterian Hospital.
The injured included five police officers who were heading to work, according to Mayor Michael Bloomberg, and a 14-year-old boy who was taking a weekend ride with his father on the same train the youngster usually takes to school.
The train's assistant conductor, Maria Herbert, suffered an eye injury and a broken collarbone, Bottalico said.
Gov. Andrew Cuomo said on NBC's "Today" show that he thinks speed will turn out to be a factor in a crash he called "your worst nightmare."
The MTA identified the dead as Donna L. Smith, 54, of Newburgh; James G. Lovell, 58, of Cold Spring; James M. Ferrari, 59, of Montrose; and Ahn Kisook, 35, of Queens. Three of the dead were found outside the train; one was inside.
Lovell, an audio technician who had worked the "Today" show and other NBC programs, was traveling to Manhattan to work on the Rockefeller Center Christmas tree, longtime friend Janet Barton said. The tree-lighting ceremony is Wednesday night.
"He always had a smile on his face and was quick to share a friendly greeting," ''Today" executive producer Don Nash said in a message to staffers.
The NTSB has been urging railroads for decades to install Positive Train Control technology. Congress in 2008 required dozens of railroads, including Metro-North, to do so by 2015.
The MTA awarded $428 million in contracts in September to develop the system for Metro-North and its sister Long Island Rail Road. But the MTA has asked for an extension on the deadline to 2018, saying it faces technological and other hurdles in installing such a system across more than 1,000 rail cars and 1,200 miles of track.
The derailment came amid a troubled year for Metro-North, and marked the first time in the railroad's 31-year history that a passenger was killed in an accident.
In May, a train derailed in Bridgeport, Conn., and was struck by a train coming in the opposite direction, injuring 73 passengers, two engineers and a conductor. In July, a freight train full of garbage derailed near the site of Sunday's wreck.
Eltman reported from Mineola, N.Y. Associated Press writers Kiley Armstrong, Verena Dobnik, Deepti Hajela, Ula Ilnytzky, Colleen Long, Jake Pearson and Jennifer Peltz contributed to this report.