Two days after improvised explosives rocked the Boston Marathon, killing three and injuring at least 170 more, investigators have reportedly arrested a suspect in the attack. [UPDATE: The Boston Police and federal officials have stated that no arrest has been made in the Boston Marathon bombing case, despite numerous news reports claiming otherwise. However, reports that a suspect has been identified have held up thus far.]

CNN, the Boston Globe, the Associated Press, and Fox News report that a suspect is in custody. However, NBC and CBS maintain that no one has been arrested. [UPDATE: CNN has walked back its initial claim, now reporting that no arrest has been made.]

Multiple news reports early Wednesday afternoon said surveillance footage obtained by investigators showed what they believe is the suspected attacker carrying and planting a backpack at the site of the second explosion. 

According to the Boston Globe, citing an official familiar with the investigation, investigators believe they are "very close" to cracking the case. That official added that authorities may announce their findings as soon as this afternoon.

A press conference is already scheduled for 5 p.m. tonight.

According to CNN, surveillance footage obtained by police led to the reported breakthrough. From CNN's Tom Watkins:

The breakthrough came from analysis of video from a department store near the site of the second explosion. Video from a Boston television station also contributed to the progress, said the source, who declined to be more specific but called it a significant development.

On Tuesday, investigators revealed that they believed the improvised explosives used in the attack were shrapnel-laden pressure cookers stuffed into backpacks.

UPDATE: The FBI has released a statement saying there is no suspect in custody:

Contrary to widespread reporting, no arrest has been made in connection with the Boston Marathon attack. 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. Since these stories often have unintended consequences, we ask the media, particularly at this early stage of the investigation, to exercise caution and attempt to verify information through appropriate official channels before reporting. [FBI]

Editor's note: The headline for an earlier version of this story stated that a suspect had been arrested, based on reports from CNN, the Boston Globe, the Associated Press, Fox News, and others. Those reports, however, seem to have been premature.