Unlike with the Boston Marathon bomber, police have a suspect in mind as they try to determine who mailed a letter to Sen. Roger Wicker that tested positive for poisonous ricin, a Senate colleague said.

Federal agents zeroed in Tuesday on how the Boston Marathon bombing was carried out.

- Arkansas plans to put prisoners to death with a drug that experts say has never been used in a U.S. execution.

Senate Majority Leader Harry Reid says a letter containing ricin or another poision was sent to the office of Sen. Roger Wicker of Mississippi.

President Barack Obama says the explosions at the Boston Marathon are being investigated as an act of terror, although authorities still don't know who is responsible.

The boy who was killed in the Boston Marathon bombings was remembered by neighbors Tuesday as a vivacious 8-year-old who loved to run and climb.

Over the next week, she pieced together one horrifying detail after another. She went online and tried to confront the three boys she had known since junior high who she believed had done it.

Republican opposition is growing to a bipartisan Senate plan for expanding background checks for firearms buyers, enough to put the proposal's fate in jeopardy.

Obama, speaking from the White House late Monday, pointedly avoided using the words "terror" or "terrorism," saying officials "still do not know who did this or why."

With more than 30 marathons this weekend and big events on the horizon, officials around the world are looking at security efforts in the wake of the fatal bomb blasts that shook Boston's race.

It dawned chilly, clear and blue, a parsimonious but perfect serving of New England springtime that — because it came on the third Monday in April — unquestionably called for a celebration.

A grand jury about to be seated in eastern Ohio will investigate whether other laws were broken in the case of a 16-year-old girl raped by two high school football players last year.

Thousands of people are expected to join an unofficial counterculture holiday celebrating marijuana in Colorado and Washington this coming weekend, including out-of staters and even packaged tours.

As Congress readies for a drawn-out immigration debate, an expanding network of Republican fundraisers is pressing for a path to legal status for millions of immigrants living in the United States illegally.

A bipartisan group of senators is almost ready to share with colleagues and voters an immigration overhaul crafted over several months.

Key measures of New York's tough new gun law are set to kick in, with owners of guns now reclassified as assault weapons required to register the firearms and new limits on the number of bullets allowed in magazines.

With the Senate set to begin debate on gun control legislation this week, a proposal to expand background checks for gun buyers picked up some key Republican support over the weekend.

DNA may be the building block of life, but can something taken from it also be the building block of a multimillion-dollar medical monopoly?

Congressional investigators say pharmacy boards in nearly all 50 states lack the information and expertise to oversee specialty pharmacies like the one that triggered a deadly meningitis outbreak last year.

The American Red Cross is responding across the South and Midwest after a severe weather outbreak that spawned tornadoes Thursday.

The driver of the bus that swerved off a North Texas highway, leaving two passengers dead and dozens injured, was at the wheel in another fatal accident 15 years ago.

Dylan Quick also told an investigator that he had researched mass stabbings on his home computer about a week before the attack at Lone Star College in Cypress, according to a search warrant affidavit.

School district spokesman Ron Lesko said administrators were discussing what official action the 10th-grade teacher at Albany High School could face for the assignment given to students on Monday.

President Barack Obama's latest plan to raise monthly Medicare premiums for upper-income retirees would significantly expand the number who would be expected to pay more.

Jonathan Winters, the cherub-faced comedian whose breakneck improvisations and misfit characters inspired the likes of Robin Williams and Jim Carrey, has died. He was 87.