The police officers in charge of the man left forgotten in a court cell this weekend are "devastated".
Wairarapa Police Area Commander Inspector Donna Howard said when the staff heard the 59-year-old man was found in the cells on Monday, their first concern was for his "health and wellbeing".
"They were devastated," she said.
"Everyone comes to work to do a good job. They obviously feel very responsible."
Howard said there were still a lot of questions regarding the incident, but believed it was a "genuine human error in terms of a breakdown of communication".
The man, who had appeared in the Masterton District Court on Saturday morning after breaching bail conditions, was left "cold, hungry, and terrified" for two days and nights.
He used his shoe for a pillow and a concrete slab for a bed.
He was found at 8.45 on Monday morning.
"He obviously heard activity around the courts, so when our police prosecutor went through, the gentleman was standing up at the door by the small viewing pane and was seen then," Howard said.
"When we were speaking with him, he was pretty traumatised -- there's no two ways about it, and very overwhelmed."
The man was taken to the police station where he was examined by a doctor, given a hot drink and some food, and was talked to by police.
"It was about giving him some wraparound support and acknowledging to him that this was on us," Howard said.
"For me it was important that he realised this was not on him. This was on us."
Police took the man back home to his family after he was "cleared" by the doctor.
Howard said the man and his wife had both acknowledged apologies from police.
"I gave him an undertaking that the priority now was to find out how it happened," she said.
"It's about figuring out what we can do better to ensure this doesn't happen again."
Howard said she called the national manager of Police Professional Conduct about mid to late morning on Monday, and they then notified the Independent Police Conduct Authority (IPCA).
IPCA general manager Warren Young said the IPCA had referred the matter back to police to investigate under the IPCA's "active oversight".
"We will also review and determine the adequacy of the investigation and its outcome when it is finished," he said.
"We have no comment about the incident at this point in the investigation."