Officials said 76 people overdosed Wednesday and 17 more fell ill Thursday.
Emergency crews showed up and found some people passed out and unresponsive, while others were complaining of nausea or were vomiting.
Hawk said the people who tested positive may have taken other drugs laced with fentanyl in addition to the synthetic marijuana, which is plant material sprayed with drugs and chemicals.
Officials were testing the blood of the victims to see exactly what they ingested. He was also charged in connection with drug sales in the city earlier this year, the chief said.
As of Wednesday afternoon, 29 people had overdosed across New Haven, city spokesperson Laurence Grotheer told TIME.
New Haven Police arrested a second suspect, 37-year-old parolee Felix Melendez, and federal authorities apprehended a third though it is unclear whether the two are connected to the overdoses.
"It's a nationwide problem", Alston said of drug overdoses.
"It's very reminiscent of a mass casualty incident", New Haven Office of Emergency Management Director Rick Fontana told the New Haven Register.
Alston said that based on the evidence at the scene, the drug was suspected to be K2, a synthetic marijuana. By late Wednesday night there had been no deaths reported. In recent months, K2 has caused hundreds of people in about 10 states to be hospitalized, sometimes with severe bleeding. Chief Mark Vendetto, New Haven Fire Department.
Synthetic opiates like fentanyl, which is 30-50 times more potent than heroin, are extremely unsafe, with high risks of overdose and death.
'We're eager to raise awareness at the highest levels of the federal government for a better sense of what happened and the challenges that urban centers face in terms of combatting a persistent, vexing presence of people with substance abuse disorder'.
The state Senate Republican leader, Len Fasano, of North Haven, criticized New Haven officials today for not addressing drug use on the Green. Multiple people who were affected by the drug identified Parker as someone who'd been dealing it in the area, Campbell said. He said the Green has become "a place of despair" and "no longer an attraction for families or economic development".