UK Anti-Doping chief David Kenworthy has criticised the answers given by cycling officials to MPs last month regarding the contents of the 'mystery' package delivered to the Team Sky doctor at a race in 2011.
Team Sky principal Sir Dave Brailsford was among witnesses to appear before the Culture, Media and Sport select committee in Westminster in December, answering questions about doping in sport.
During his testimony to MPs, Brailsford said he believed the package delivered to Team Sky doctor Richard Freeman at the end of the 2011 Criterium du Dauphine in France contained the decongestant Fluimucil -- a drug that is not banned in sport.
That package, delivered by British Cycling employee Simon Cope and intended for use by star rider Sir Bradley Wiggins, has been the subject of a UKAD investigation into alleged wrongdoing ever since the story was revealed by the Daily Mail in October.
Prior to Brailsford's comments, British Cycling president Bob Howden, chair of the British Cycling ethics commission Dr George Gilbert and former Team Sky coach Shane Sutton had all been asked by Committee chair Damian Collins MP about the package, but none of the three had been able to offer any new information.
Speaking to the BBC, outgoing UKAD chairman Kenworthy said he found the evidence given at the hearing "extraordinary" and "very disappointing", and said there is still no definitive answer about what the package contained from anybody who was involved.
Kenworthy also insisted UKAD is continuing its investigation and will "dig and delve" to find out what was in the package.
He said: "I watched the select committee hearing, which I thought was extraordinarily fascinating.
"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. 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.
"It's not that I don't believe it, it's just the fact that so far away from it, people remember a whole lot of detail but not the actual crucial bit, which was in the package."
Regarding Brailsford's explanation that the package contained Fluimucil, Kenworthy said: "Well that's what Dave Brailsford came out with at the hearing, but he didn't actually say 'I know that's what it was', he said 'I've been told that's what it was', so there's still no definite answer from anybody who was involved."
He added: "But we'll dig and delve, we're not giving up on this, and we'll find out what's in that package."
"One of the tragedies of all this is that you've got probably the greatest cyclist [Wiggins] that the UK has produced in years, he's just coming to his retirement and all the talk is not about the successes that he's had, but about this package. It just undermines yet again the joy of sport."
Team Sky has continually denied any wrongdoing and has say it is "confident" it will be cleared of any wrongdoing when UKAD completes its investigation. There is no suggestion of any wrongdoing by Wiggins and British Cycling has said it cannot comment while the UKAD investigation continues.
On Friday, Team Sky's current star rider, the three-time Tour de France winner Chris Froome, was asked about the ongoing story.
The Guardian reported that Froome was asked whether Brailsford's ability to defend his own riders against allegations of doping had been damaged as a result of the saga and that he replied: ''That's not for me to say. You'd have to ask [him] that.''
He added: ''Dave himself has put his hand up and said he has made mistakes. I think if you look at what Dave has actually done, the team he has put together, I think we've got a great group of guys with values in the right place.''