A man died without his relatives knowing after a mix up led to another family turning off his life support.

Relatives say Elisha Brittman, 69, was misidentified as Alfonso Bennett after he was found naked and unresponsive with serious facial injuries beneath a car in Chicago in April.

He was taken to Mercy Hospital, where he was listed as John Doe while his family continued their desperate search for him, according to the CBS 2 news channel.

Mr Bennett’s family later received a phone call from the hospital, which said he had been identified through mugshots and that he was in intensive care.

When he showed no signs of improvement, the Bennett family agreed to have his ventilator removed and he died days later.

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The family were in the middle of arranging the funeral when the real Alfonso Bennett turned up at a barbecue.

Mr Brittman’s relatives, who still believed he was missing at the time, learned of his death after he was eventually identified through fingerprints at the morgue.

Both families have now filed a wrongful death lawsuit against the City of Chicago and Mercy Hospital, accusing them of negligence.

Still image of Elisha Brittman taken from a video by CBS Chicago. (CBS Chicago)

They say the mix up, which has been devastating for everyone involved, may never have happened if Mr Brittman had been fingerprinted in the first place.

Mr Bennett’s sister Rosie Brooks, who received the phone call saying her brother was in hospital, told a press conference on Wednesday: “I said ‘how did you all verify this was Alfonso Bennett’ –they said ‘through the Chicago Police Department’.

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“In my heart I could not recognise him.”

She added: “If this [the fingerprinting] had been done when they first picked that body up we wouldn’t even be here today.”

State senator Patricia Van Pelt said she would look into introducing legislation which would require an unconscious person to be identified through fingerprints.

Anthony Guglielmi, chief communications officer for Chicago Police, said in a tweet last month: “To say that we currently have questions is an understatement.

“We have detectives looking into every aspect of this incident – from the incident response to the circumstances leading to the hospitalisation and the notification of family members.”

A spokesperson for Mercy Hospital said it would not be providing a statement at this time.