So. There is apparently an "ongoing security concern".
According to Sheriff Benny House:
“The FBI were up there. What their purpose was nobody will say.”
Steven Aftergood, who heads an organization that challenges government secrecy in science said:
“New Mexico is a center of national-security-related science, and for that reason it has also been a prominent venue for foreign espionage”
When asked about biohazard material or other mail related terror, the local spokesman for the US Postal Service Rod Spurgeon had this to say:
“I haven’t heard of anything like that going on”