Vance, who was joined by NYPD Commissioner Bill Bratton, said the 175 phones his office is unable to unlock cover a wide range of cases, including homicide, attempted murder and sex abuse cases.
He said having access to the phones would allow detectives to see messages, videos and contact lists showing how alleged co-conspirators are connected -- and also serve the purpose of helping to exonerate the wrongfully accused.
"It is very difficult to explain to a victim of a crime ... that we cannot get the evidence that may identify the individual who may have committed the crime," Vance said.
"When Apple made its decision in the late fall of 2014 to lock their devices through end-to-end encryption, I was aware immediately this was going to have an impact in the DA’s office," Vance said.
The news conferences comes as Vance published an op-ed in the New York Times calling iPhones "the first warrant-proof consumer products in American history."
"But as the encryption debate zeroes in on the cowardly terrorist acts committed in San Bernardino, we should also remember that Apple’s switch to default device encryption affects virtually all criminal investigations, the overwhelming majority of which are handled by state and local law enforcement," Vance wrote. "Our agencies do not have the same resources as the federal Justice Department, which is why a national, legislative solution is so urgently needed."