The death is believed to have happened two weeks ago when the detainee had a seizure during intake at Delaney Hall.
He was released from ICE custody on the spot and sent to the hospital where he was pronounced dead.
ICE is required to notify Congress and the public if someone dies in their custody, but technically, according to ICE, the third death did not happen there.
"In their custody is a particular way of thinking that ICE has in terms of people that are in their custody, but they can release them on a discretionary basis," Menendez said. "Once they do so, they're no longer responsible for even reporting the death."
Menendez said he became aware of the third death during an unannounced oversight visit after the death of Edwin Lopez-Cornejo on Saturday.
Federal authorities told Lopez-Cornejo's family that the 39-year-old died after being transported from the facility, but family members believe he had already died before arriving at the hospital.
"There's the information that ICE provides and then what I've often found to be a separate reality that we hear from the detained individuals, their families and advocates, and they often don't line up," Menendez said. "I personally choose to believe the detained individuals, their families, rather than ICE."
On Thursday afternoon, Eyewitness News cameras were rolling when emergency medical crews responded to two separate calls at Delaney Hall.
A patient was taken away on a stretcher at about 12:30 p.m. About an hour later, another ambulance arrived and transported a second patient.
The medical conditions of the patients and whether they were detainees were not yet known.
Eyewitness News has reached out to Homeland Security and ICE but we have not yet heard back.
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