The investigation into the bombing of the Boston Marathon accelerated Wednesday with reports that authorities are seeking a man who left a black bag near one of the blast sites.
A media frenzy began mid-Wednesday afternoon when CNN reported that an arrest in the case had been made or was imminent.
The FBI responded with a sharply worded statement dismissing those reports.
"Contrary to widespread reporting, no arrest has been made in connection with the Boston Marathon attack," said Special Agent Greg Comcowich in the statement. "Over the past day and a half, there have been a number of press reports based on information from unofficial sources that has been inaccurate."
A media briefing scheduled for 5 p.m. Wednesday evening was postponed. It is not publicly known when the next briefing will occur.
Major metropolitan areas have been on edge since Monday afternoon when two explosions near the marathon finish line killed three and wounded more than 170 people.
On Tuesday it was revealed that traces of the toxic poison ricin had been detected on a letter sent to the office of Sen. Roger Wicker (R., Miss.). On Wednesday the FBI confirmed that a second letter, this one sent to the White House, had been intercepted at an off-site mail facility also for containing substances that tested positive for ricin.
"There is no indication of a connection to the attack in Boston," the FBI national press office said in a statement Wednesday.