In a BBC interview published on Saturday, outgoing UKAD chairman David Kenworthy said his evidence was underwhelming.
The head of UK Anti-Doping (UKAD) has criticised Team Sky over their inability to prove what was in a package delivered to a team doctor during a 2011 race.
UKAD is investigating the package, intended for Bradley Wiggins during the 2011 Criterium du Dauphine, and Team Sky principal Dave Brailsford was grilled about it during a British parliamentary hearing last month.
He could only say he had been told it contained a legal decongestant, Fluimucil, but in a BBC interview published on Saturday, outgoing UKAD chairman David Kenworthy said his evidence was underwhelming.
"What you had here was an incident which occurred in 2011 and the hearing was in December 2016, so five years ago people can remember a package that was delivered to France," Kenworthy said.
"They can remember who asked for it, they can remember the route it took, who delivered it, the times it arrived.
"Everybody can remember this from five years ago, but nobody can remember what was in the package. That strikes me as extraordinary.
"It's very disappointing. We're still continuing the investigation."
British Cycling president Bob Howden, the body's ethics commission chair George Gilbert and ex-Team Sky coach Shane Sutton were unable to divulge the contents of the package when asked by British lawmakers.
Kenworthy said UKAD would continue to "dig and delve" until it found out what was in the package.
Team Sky and their former star rider Wiggins, who retired last month, have consistently denied wrongdoing.
British Cycling, which shares a Manchester headquarters with Team Sky, has said it cannot comment while the UKAD investigation is ongoing.