Assistant Police Commissioner Justin Meyers tells Fox 5 News that the victims, "suffered significant trauma through their bodies".
Crime scene investigators remained on the scene early on Thursday, blocking off several surrounding streets.
The men's badly beaten bodies were found inside Recreation Village Town Park in Central Islip sometime Wednesday. "I have full confidence that the outstanding men and women of the Suffolk County Police Department under the leadership of Commissioner Tim Sini and Chief Stuart Cameron will do what is necessary to apprehend the perpetrators and bring them to justice".
"It appears they were killed with a sharper-edged instrument", Sini said.
Investigators linked the murders to MS 13 gang members and arrested eight suspected gang members in March.
Prosecutors said Kayla Cuevas, 16, was targeted last summer by a group of four gang members because she had been feuding with MS-13 members at school and on social media.
He did reveal that they are all males - one 16-year-old, two 18-year-olds and one 20-year-old.
The distraught family and friends of two missing Long Island teens fear the boys have been killed by MS-13 gang members - and that their loved ones are among the four bodies found overnight in a park.
Gang violence has been a problem in areas like Central Islip and Brentwood, but Suffolk County police and the Federal Bureau of Investigation began pouring resources into a crackdown after the killings of two Brentwood High School girls in September.
Emergency vehicles are parked near the site where four bodies were discovered in Central Islip, N.Y., Thursday, April 13, 2017. "I don't know what it is, but it's definitely getting worse".
MS-13, which was founded in Los Angeles by immigrants fleeing the violence in El Salvador during the 1980s, is one of the largest criminal organisations in the U.S., reports CNN. It grew after some members were deported to El Salvador, helping turn that country into one of the most violent places in the world. It's now a major worldwide criminal enterprise with tens of thousands of members in several Central American countries and many US states.
The bodies were found just a few miles from where police say MS-13 gang members killed numerous people, including Brentwood High School students Nisa Mickens and Kayla Cuevas previous year. He promised as much in a Time interview, referencing a Newsday story about the killings. The girls had gone for a walk the night they were killed, CNN affiliate News 12 Long Island reported.