In espionage (and police work,) evidence of covering up a crime is often more obvious than the crime itself. Unfortunately, no one has easy access to these sites, so while we have secondary evidence, Iran is covering up the primary evidence.
And, at Parchin, they are doing it again.
From ISIS:
Recent commercial satellite imagery of the Parchin site in Iran shows the extent of new paving as well as the extent of other alternations undertaken at the site over the past year and a half starting in February 2012. Iran appears to be in the final stages of modifying the suspected high explosive test site at the Parchin complex, having recently asphalted large sections of the site. As noted in several of the International Atomic Energy Agency’s (IAEA’s) quarterly Iran safeguards reports and in numerous ISIS satellite imagery reports on Parchin, asphalting and the other documented activities have significantly changed the site and impacted the ability of IAEA inspectors to collect environmental samples and other evidence that it could use to determine whether nuclear weapons-related activities once took place there. Asphalting an entire area in this manner would make it very hard to take soil samples and likely be effective at covering up environmental evidence of nuclear weaponization-related experiments. Iran in 2003 and 2004 conducted similar concealment activities at Lavisan-Shian, razing and rebuilding the entire site in an effort suspected to be aimed at concealing alleged, undeclared military nuclear efforts.Iran is banking on the West discounting secondary evidence. And the scheme works well.
The Parchin site remains of interest to the IAEA due to evidence of pre-2004 activities related to the development of nuclear weapons. Iran is alleged by the IAEA, the United States, and at least three European governments to have had a well-structured nuclear weapons program aimed at building a warhead small enough to fit on the Shahab 3 ballistic missile.
"Hey, IAEA, look over there for a minute, will you? I have to, um, take out the trash."