The former eye surgeon was acquitted last year of the murder of his wife Pauline Hanna at their Remuera home in 2021, but was sentenced to 150 hours of community work for possession of methamphetamine.
The trial lasted eight weeks and heard from 80 witnesses before the verdict was delivered.
On Sunday, the NZ Herald reported that Seymour wrote to police Auckland District Commander Karyn Malthus in 2022 after he was approached by Polkinghorne with concerns about his treatment.
"Mr Polkinghorne has had a harrowing and traumatic experience, but feels he has been treated like a suspect rather than a traumatised member of the public," the letter stated.
"It's understandable that police would regard him as a person of interest. But in this instance, the police appear to have gone beyond that brief. While acknowledging the difficult balance police must strike, Mr Polkinghorne feels that he has been subject to prejudice from the police in the above actions."
"An electorate MP's job is to serve their constituents. I had a constituent contact me with concerns over the way they felt they had been treated by police. As is made clear in the letter, the intention was to pass on the constituent's concerns to police," he said in a statement on Sunday.
His office also said it doesn't comment on donations or share further information on constituency cases due to privacy reasons.
