While the nation’s attention is fixed on the horrific bombings of the Boston Marathon, another terror-style event with the potential for lethal results is taking place in Washington, D.C.

There, letters testing positive for the deadly poison ricin, for which there are treatments but no reliable antidote, have been discovered. One was addressed to a Republican senator, Roger Wicker of Mississippi, and the other to President Obama.

The letters, which contained identical phrasing about the necessity of taking action against “wrong,” are said to have been sent by a person who often communicates with public officials.

In addition, three “suspicious” parcels were intercepted by the Capitol mail office, a facility in Maryland established to screen officials’ mail after the anthrax attacks of 2001.

And the offices of two senators, Carl Levin, D-Mich., and Jeff Flake, R-Ariz., said they had turned two other envelopes over to authorities.

Ricin, a protein inhibitor extracted from castor beans, is deadly even in amounts as small as a few grains of table salt if inhaled, ingested or injected. It is relatively simple to make and castor beans can easily be grown at home, meaning that control of its production is nearly impossible.

Ricin figured in chemical warfare research in the past, and was implicated in some attempted and actual assassinations of dissidents by Soviet bloc agents, but never has been widely produced as a weapon because other chemicals were deemed more suitable to military use.

If authorities do know who is responsible for the letters, it seems likely that person is already in custody or will be shortly — although more letters or packages could still be wending their way through postal channels.

Nobody should relax until the threat has been fully addressed. We may live in an age when individuals can do a lot of damage with simple substances, but we shouldn’t assist them by being complacent or naive.