A “package containing a substance” was delivered to St. James’s Palace on Feb. 12, according to the Metropolitan Police. Harry’s offices are located there.
Authorities tested the substance and determined it was “non-suspicious.”
Detectives are investigation “an offense of malicious communication” related to the package. According to London’s Evening Standard, the package contained a racist message.
Prince Harry and Markle are set to be married May 19 at Windsor Castle.
Earlier this month, a letter containing a white powder was sent to Parliament, which caused a partial evacuation.
That powder was also found to be non-toxic.
(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)