Key Points:

A top lawyer has contacted a former cop who claims he lied in court and sent at least 150 people to jail wrongfully.

Police have hired leading Wellington lawyer Bruce Squire QC to investigate Patrick O'Brien's confession that he committed perjury by lying as a Crown witness in drugs trials in the 1970s and tampered with evidence.

Squire was appointed in March, and wrote to O'Brien asking about the nature of the lies and the names of the defendants in the court cases.

After getting no reply, he emailed again and advised O'Brien he was busy for six weeks with trial commitments.

In April, O'Brien wrote back: "Kindly advise by return email the time, date and location of venue, convenient for your purpose, that we may arrange an appointment."

Squire replied this week, a few days after the Herald on Sunday reported O'Brien's claims. O'Brien emailed back and apologised for not answering Squire's questions. "I assumed the answers were self-evident from a reading of my original confession," he wrote.

He said the nature of his lies were "most grievous". He considered them perjury and a "mortal sin" but did not know the names of his targets.

Police have refused O'Brien's request for the names of the cases he worked on, citing privacy reasons.

Police spokesman Jon Neilson declined to comment on the apparent lack of progress in the nine months since Squire's appointment as the inquiry was ongoing.