Production started almost two years after it's lead star died. Therefore, Peter Sellers features in archive footage only, with deleted scenes; coming from The Pink Panther Strikes Again (1976), and old footage; coming from all the previous Pink Panther movies.
In spite of the screenplay credits for Frank Waldman and Tom Waldman, the two actually contributed nothing to the script. Their credit was solely as a result of usage of the deleted scenes from The Pink Panther Strikes Again (1976) (which the latter made some uncredited contributions to).
This movie is compiled from outtakes and deleted scenes from five previous Pink Panther movies featuring Peter Sellers. New material involving other actors other than Peter Sellers was filmed for the movie. Some of the older material dated as far back as eighteen years before this movie was made, to around 1964. Reportedly, at the time of theatrical release, some of the archival footage of Peter Sellers Inspector Clouseau had never been seen widely before.
The widow of Peter Sellers, Lynne Frederick, allegedly sued Blake Edwards and this movie's producers claiming that this movie allegedly diminished the late Seller's memory / reputation. Frederick's lawsuit was allegedly successful and with a reported settlement of US $1+ million.
If Peter Sellers had not passed away, then this film would not allegedly have been made (at least at around this time). The next intended Pink Panther film that was being planned prior to Sellers' passing was entitled Romance of the Pink Panther.
All of the outtakes come from "The Pink Panther Strikes Again" but Blake Edwards had hoped to also utilize outtakes from "Return Of The Pink Panther". He had cast Peter Arne and Gregoire Aslan who had been in "Return" to appear in linking material for "Trail" but Aslan died before production began and Edwards also wasn't able to secure rights to the outtakes. In the end, Harold Kasket replaced Aslan while Arne effectively played a different looking character not needed to match old footage.
Edwards had originally hoped to construct a Citizen Kane-esque narrative, with Clouseau having gone missing at the very beginning of the story, whilst the memories of the supporting characters would showcase the deleted or unused content as the shooting scripts for Return, Strikes Again, and Revenge demonstrated a great amount of comedic material that was left on the cutting room floor. Unfortunately, MGM/UA were unwilling to pay ITC the fee they were asking for the Return outtakes, and Edwards fell behind schedule on Trail/Curse (MGM/UA also ended up reducing both films' budgets considerably), with the result being that Trail failed to live up to its potential.
Clouseau's father tells the reporter, around 1:26:20, "My son, Jacques Clouseau, was born September 8th, 1920." This is the same birthday that Peter Sellers has, except he was born five years ahead of Clouseau's.