UK police were concerned Andrew Mountbatten-Windsor could block searches at his properties by claiming officers must obtain permission from King Charles, newly released court files show.
Thames Valley Police has acknowledged the search warrants used to raid Andrew's residence on the Sandringham Estate and his former Windsor home, Royal Lodge, in February were unlawful.
Andrew had challenged the warrants, and documents from the ensuing High Court proceedings revealed police feared evidence could be lost if they had to seek permission from Buckingham Palace first to search the premises.
Detectives were searching for "paperwork, diaries, business records or other documentary evidence of AMW's time as Special Representative for Trade and Investment", documents show.
According to Andrew's lawyers, police told the Old Bailey judge: "AMW or his legal team may seek to advance that the property belongs to someone else (the King) and that separate legal permission should be sought."
"Obtaining such consent may not be expeditious and seeking to do so in advance may frustrate the nature and purpose of the search."
According to the same documents, police considered Andrew a suspect "in a number of serious offences", including forwarding official reports to US pedophile financier Jeffrey Epstein "within minutes of receiving them".
The reports related to Andrew's official trips as trade envoy to Singapore, Vietnam, China and Hong Kong in October 2010.
The documents also contained a statement from the detective chief inspector in charge of the raids at Andrew's properties.
The DCI, whose identity was not disclosed, told the judge: "My investigative objectives are to secure relevant evidence in a timely and secure fashion.
"Failure to do so risks loss of evidence and a consequent loss of public trust and confidence in the investigation.
"AMW and or his representatives may or may not be in a position to grant access to the premises, either way I cannot risk not have an appropriate legal power to achieve my objectives."
Police also argued it was a "matter of public record" that Andrew "has previously not engaged with other investigative strands relating to his alleged involvement with Jeffrey Epstein."
Andrew's lawyers denied the allegation, adding that police never contacted the former prince or his legal team to ask whether they would grant access to the residences "or any relevant evidence".
The former Duke of York was arrested on suspicion of misconduct in public office on February 19, his 66th birthday, following allegations he shared sensitive information with Epstein during his time as the UK's trade envoy.
Andrew was interviewed under caution before being released under investigation, and denies wrongdoing, with the police probe ongoing.
Justice Hilliard said last week while the King's younger brother and Thames Valley Police have reached an "agreement" the warrants were unlawful, police have since launched a bid to retain evidence gathered during the searches in February.
He said Andrew opposes the bid to retain the evidence, with a hearing in the case to be held in private in 2027.
It means the former prince could remain in limbo for several more months before learning if he will be charged with an offence.