Double-murderer Jason Reihana was treated at Waikato Hospital earlier this month next to patients unaware they were sharing a ward with a convicted criminal.
Reihana, who was jailed for life in 2007, was spotted at the hospital in early February by an unnamed person who had been visiting another man on the ward, Fairfax has reported.
A spokeswoman for Waikato District Health Board told the Herald they were unable to confirm whether Reihana was in the hospital and said they couldn't comment on his treatment for privacy reasons.
Reihana was convicted of murdering his former partner, Teresa Gunn, the mother of his two sons, and her new boyfriend Andrew Grabner in a frenzied knife attack in Tauranga on December 11, 2005.
Armed with three knives, he drove from his Te Kawa home and killed them both in a frenzied attack.