NPR News

Update at 8:44 p.m. ET. Authorities Make An Arrest:

Authorities have made an arrest in connection to the suspicious envelopes sent to a senator and President Obama.

The FBI identified the suspect as Paul Kevin Curtis.

The The Clarion Ledger reports:

Quoting "congressional and law enforcement sources," CNN is reporting that an envelope sent to a senator's office has tested positive for the poison ricin.

"After the envelope tested positive in a first routine test, it was retested two more times, each time coming up positive, the law enforcement source said," CNN reports. "The package was then sent to a Maryland lab for further testing."

Monday's explosions in Boston have led to heightened security elsewhere, with New York, Washington and Los Angeles among the cities taking action within hours of the blasts.

"We're stepping up security at hotels and other prominent locations in the city through deployment of the NYPD's critical response vehicles until more about the explosion is learned," Paul J. Browne, the deputy commissioner of the New York Police Department, .