It was already well known that the FBI was talking with and investigating May First/People Link. Whoever is sending in the bomb threats to U Pittsburgh already

It was already well known that the FBI was talking with and investigating May First/People Link. Whoever is sending in the bomb threats to U Pittsburgh already knows it as well. So there was no point in 'staking out' this server. They probably just seized it for evidence collection. May First/People Link said they don't keep any logs. Maybe the FBI didn't believe them or think they can do some 'advanced forensics' on the HDD.