Sullivan, now 68, was only freed when the DNA profile from an unknown man was found in 2023 in semen samples taken from the scene of the attack.
The results of the new tests were not disputed by the Crown Prosecution Service (CPS) and he was freed by the Court of Appeal in May 2025.
The IOPC watchdog contacted Merseyside Police in July 2025 to ask about the case, and were told the force had received no formal complaints and had not identified any potential misconduct by officers from the time of the original investigation.
However, in November, Sullivan gave his only media interview to the BBC and claimed he had been “stitched up” after his arrest, including being fed information to make his false confession sound plausible.
He said he was interviewed seven times without a solicitor present and was threatened with being charged with “35 other rapes” if he did not confess.