The latest search turned up multiple skeletal remains, which have been turned over to the chief medical examiner, according to James Wardwell, New Britain chief of police.
Investigators believe that one person is responsible for the deaths, Wardwell said.
The suspect who killed the individuals at separate times would "fit the definition" of what a serial killer is, New Britain State Attorney Brian Preleski said Monday.
"There is no danger to the public at the time from the alleged serial killer," Wardwell said without elaborating on who they believe the suspect to be.
"The ongoing investigation supports our strong belief that the person responsible for this is not able to continue this conduct at this time," he added.
A law enforcement official briefed on the investigation said a suspect in the killings is in jail on an unrelated case.
One of the four remains found in the latest search, which began in early April and concluded in the first week of May, has been identified as Melanie Ruth Camilini, Wardwell said. She was last seen in a nearby town in January 2003.
The announcement comes on what would have been Camilini's 42nd birthday.
Annual searches have been conducted in this area, described as "swampy" and "wooded," off a major highway since 2007, when a hunter alerted authorities to the remains, according to Wardwell.
The medical examiner determined then that the remains were of three women, Wardwell said. The office later identified Diane Cusack as a victim in 2010. Joyvaline "Joy" Martinez and Mary Jane Menard were identified separately in 2013, Wardell added.
All three of those women were last seen in 2003 as well, he said.
The authorities still investigating the case say that the remains recovered in the latest search have been in the area for at least 10 years and are consistent with those they found years ago.
New Britain is southwest of nearby Hartford, the state's largest city.