Investigators believe four letters sent to state offices containing some powder are related and they think they have a good lead.
State Patrol spokesman Lance Clem says at least one of the envelopes had information that will make it "interesting and easy to investigate." He didn't not elaborate.
The letters led to evacuations at three buildings in downtown Denver yesterday and another at a building in Lakewood that's home to the call center for the state patrol.
The substances in all four cases turned out to be harmless.
Authorities don't believe these incidents are connected to a suspicious powder found at a Denver bank on Sunday.