A letter addressed to President Barack Obama tested positive for the poison ricin and was from the same sender who mailed a letter to a senator that also tested positive, officials told NBC News on Wednesday.

The letter to Obama was intercepted at an off-site White House mail facility and was being tested further, the FBI said. A federal law enforcement official said that the letter was “very similar” to one addressed to Sen. Roger Wicker, R-Miss.

Federal officials told NBC News that they believe they know who sent the letters, but no arrest was made because authorities were waiting for further test results.

Ricin is made from castor beans and can kill within 36 hours. There is no antidote. Some threatening letters simply contain ground castor beans, resulting in a positive field test for ricin without the concentrated poison. Results from full laboratory tests are expected in the next 24 to 48 hours.

Filters at a second government mail screening facility also tested positive for ricin in preliminary screening Wednesday.

An FBI official told NBC News that the agency did not initially believe the letters were related to the attack on the Boston Marathon on Monday.

Authorities cleared the atrium of a Senate office building Wednesday and were investigating a suspicious package there. Capitol police were also investigating a suspicious package at the office of Sen. Richard Shelby, R-Ala. Shelby’s staff had not been evacuated.

The Wicker letter was postmarked Memphis, Tenn., and had no return address. The FBI confirmed the preliminary positive test on it Tuesday. That letter was intercepted at a postal facility in Maryland that screens mail sent to Congress, and never reached Wicker’s office.

Other senators were made aware of the Wicker letter during a briefing Tuesday evening on the bombing in Boston. Sen. Claire McCaskill, D-Mo., said that the person who sent Wicker the letter writes often to elected officials.

People can be exposed to ricin by touching a ricin-laced letter or by inhaling particles that enter the air when the envelope is opened. Touching ricin can cause a rash but is not usually fatal. Inhaling it can cause trouble breathing, fever and other symptoms, and can be fatal.

Field tests are conducted anytime suspicious powder is found in a mail facility, and the FBI cautioned that field tests and other preliminary tests can produce inconsistent results. When tests show the possibility of a biological agent, the material is sent to a laboratory for full analysis.

Russell Brand has apparently not been invited to become a member of the Church of Scientology. He told "Conan" that he tried to get their most famous member to recruit him while they worked together on "Rock of Ages," but either his pleas fell on Tom Cruise's deaf ears, or Cruise knew better than to take him seriously.

"Every so often, I’d say thing like, ‘Tom, sometimes I’m a bit lost in life.’ See if he would try and get me," Brand told Conan O'Brien. "That man had no interest in getting me in Scientology at all." Or, as Vulture put it, "Cruise just left him hanging on a thread of fabricated despondency."

The more the comedian thought about it, the more it seemed to bother him. "If there’s a cult that don’t want me, I want to know why," he said. Maybe he can convince Tom Cruise to come on his talk show, "Brand X," and discuss it. But probably not.

Either way, it could make for a fun future topic on "Brand X with Russell Brand," airing Thursdays at 11 p.m. ET on FX. "Conan" airs at the same time every weeknight over on TBS.

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Government laboratories are testing samples of a suspicious substance found in letters at off-site White House and Senate mailrooms after preliminary test results pointing to the deadly poison ricin rattled Washington, authorities said Wednesday.

White House mail handlers identified a "suspicious substance" Tuesday in a letter addressed to President Barack Obama that preliminarily tested positive for ricin, the FBI said. The same day, a similar letter addressed to Sen. Roger Wicker, R-Mississippi, tested positive for ricin -- a toxin with no known antidote, officials said.

But the FBI said initial tests can be "inconsistent," and the envelopes have been sent off for additional tests.

Meanwhile, Sen. Carl Levin, D-Michigan, says one of his home-state offices received a "suspicious-looking" letter and alerted authorities. "We do not know yet if the mail presented a threat," said Levin, the chairman of the Senate Armed Services Committee.

Filters at a government mail-screening facility preliminarily tested positive for ricin Wednesday morning, an FBI statement said, and mail from that site is being tested.

Mail for members of Congress and the White House has been handled at off-site postal facilities since the 2001 anthrax attacks. But Capitol Police were checking out reports of suspicious packages or letters in two Senate office buildings and evacuated the first floor of one those buildings Wednesday afternoon.

Police questioned a man in the area who had a backpack containing sealed envelopes, but a federal law enforcement official told CNN that authorities do not believe the man was connected to the letters found Tuesday.

In a statement issued Wednesday, the FBI said it has no indication of a connection between the tainted letters and Monday's bombings at the finish line of the Boston Marathon. But the discoveries further heightened security concerns at a time when Congress is considering politically volatile legislation to toughen gun laws and reform the immigration system.

The pair renewed their vows in an intimate ceremony in St. Lucia on April 13, according to Us Weekly. The couple -- who have been married for nearly eight years -- rented out the island's entire Sugar Beach Resort for the weekend in honor of the happy occasion.

Around 50 guests, including Damon's BFF Ben Affleck and his wife Jennifer Garner, looked on as the Damons said "I Do" under thatched roofs right at sunset. Reportedly, the groom, 42, wore a tan-colored suit and flip-flops, while the bride, 36, donned a cream-colored gown featuring a sequined belt at the waist.

The couple's daughters -- Isabella, 6, Gia, 4, Stella, 2, and Alexia, Luciana's teenage daughter from a previous relationship -- were in attendance and wore light-colored dresses to match their mom. After the 15-minute ceremony, guests -- who all wore shades of cream and ivory -- were escorted onto the beach for a cocktail reception.

The Damons first tied the knot at City Hall in NYC in Dec. 2005, but have been looking to renew their vows in front of friends and family.

On his 31st birthday, Chris Holmes — now known to the public as "Mr. Cake" — decided it was time to quit his job as a Border Agency official at London's Stansted Airport to do something he's passionate about and would allow him to spend more time with this family. For Holmes, this meant pursuing a cake business called Mr. Cake and notifying his employers with actual icing on a cake.

Holmes' sweet resignation letter quickly went viral when his brother-in-law tweeted a picture of it to the world. Note the bottom of the cake has a nice plug for his business, so this is great marketing as well:
In an interview with Elodie Harper at Sawston's local news station ITV news, Holmes said that his deision "seemed like the obvious choice."

"... Having set up a cake company, I thought I would leave them with a memento that would be a nice way of remembering me. I had the idea six months ago so I've kept it to myself since then."

"I think [my boss] was pleasantly surprised, of all the resignations businesses get, I think that's probably a nice way for an employee to leave and I hope they enjoyed the cake as well as the resignation."

As we now move into the official Political Aftermath period of the Boston bombing — the period that will determine the long-term legislative fallout of the atrocity — the dynamics of privilege will undoubtedly influence the nation’s collective reaction to the attacks. That’s because privilege tends to determine: 1) which groups are — and are not — collectively denigrated or targeted for the unlawful actions of individuals; and 2) how big and politically game-changing the overall reaction ends up being.

This has been most obvious in the context of recent mass shootings. In those awful episodes, a religious or ethnic minority group lacking such privilege would likely be collectively slandered and/or targeted with surveillance or profiling (or worse) if some of its individuals comprised most of the mass shooters. However, white male privilege means white men are not collectively denigrated/targeted for those shootings — even though most come at the hands of white dudes.

Likewise, in the context of terrorist attacks, such privilege means white non-Islamic terrorists are typically portrayed not as representative of whole groups or ideologies, but as “lone wolf” threats to be dealt with as isolated law enforcement matters. Meanwhile, non-white or developing-world terrorism suspects are often reflexively portrayed as representative of larger conspiracies, ideologies and religions that must be dealt with as systemic threats — the kind potentially requiring everything from law enforcement action to military operations to civil liberties legislation to foreign policy shifts.

“White privilege is knowing that even if the bomber turns out to be white, no one will call for your group to be profiled as terrorists as a result, subjected to special screening or threatened with deportation,” writes author Tim Wise. “White privilege is knowing that if this bomber turns out to be white, the United States government will not bomb whatever corn field or mountain town or stale suburb from which said bomber came, just to ensure that others like him or her don’t get any ideas. And if he turns out to be a member of the Irish Republican Army we won’t bomb Dublin. And if he’s an Italian-American Catholic we won’t bomb the Vatican.”

Because of these undeniable and pervasive double standards, the specific identity of the Boston Marathon bomber (or bombers) is not some minor detail — it will almost certainly dictate what kind of governmental, political and societal response we see in the coming weeks. That means regardless of your particular party affiliation, if you care about everything from stopping war to reducing the defense budget to protecting civil liberties to passing immigration reform, you should hope the bomber was a white domestic terrorist. Why? Because only in that case will privilege work to prevent the Boston attack from potentially undermining progress on those other issues.

Federal agents zeroed in Tuesday on how the Boston Marathon bombing was carried out — with kitchen pressure cookers packed with explosives, nails and other lethal shrapnel — but said they still didn't know who did it and why.

An intelligence bulletin issued to law enforcement and released late Tuesday included a picture of a mangled pressure cooker and a torn black bag the FBI said were part of a bomb.

The FBI and other law enforcement agencies repeatedly pleaded for members of the public to come forward with photos, videos or anything suspicious they might have seen or heard.

"The range of suspects and motives remains wide open," Richard DesLauriers, FBI agent in charge in Boston, said at a news conference. He vowed to "go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime."

President Barack Obama branded the attack an act of terrorism but said officials don't know "whether it was planned and executed by a terrorist organization, foreign or domestic, or was the act of a malevolent individual."

Scores of victims remained in hospitals, many with grievous injuries, a day after the twin explosions near the marathon's finish line killed three people, wounded more than 170 and reawakened fears of terrorism. A 9-year-old girl and 10-year-old boy were among 17 victims listed in critical condition.

Heightening jitters in Washington, where security already had been tightened after the bombing, a letter addressed to a senator and poisoned with ricin or a similarly toxic substance was intercepted at a mail facility outside the capital, lawmakers said.

There was no immediate indication the episode was related to the Boston attack. Senate Majority Leader Harry Reid said the letter was sent to Republican Sen. Roger Wicker, of Mississippi.

Officials found that the bombs in Boston consisted of explosives put in ordinary 1.6-gallon pressure cookers, one with shards of metal and ball bearings, the other with nails, according to a person close to the investigation who spoke on condition of anonymity because the probe was still going on. The bombs were stuffed into black duffel bags and left on the ground, the person said.

DesLauriers confirmed that investigators had found pieces of black nylon from a bag or backpack and fragments of BBs and nails, possibly contained in a pressure cooker. He said the items were sent to the FBI laboratory at Quantico, Va., for analysis.

The FBI said it is looking at what Boston television station WHDH said are photos sent by a viewer that show the scene right before and after the bombs went off. The photo shows something next to a mailbox that appears to be a bag, but it's unclear what the significance is.

"We're taking a look at hundreds of photos, and that's one of them," FBI spokesman Jason Pack said.

Investigators said they haven't determined what was used to set off the explosives.