Breaking: CNN, Boston Globe Say a Suspect Has Been Identified in the Boston Bombing (UPDATE: No Arrest Made)

"Substantial progress" is reportedly being made in the investigation.

(CNN) -- [Breaking news update at 1:01 p.m. Wednesday ]

Investigators believe they have identified a suspect in the Boston Marathon bombings, a source who has been briefed on the investigation told CNN's John King.

[Breaking news update at 12:52 p.m. Wednesday ]

"Substantial progress" has been made in the criminal investigation into Monday's marathon bombings, a Boston law enforcement source told CNN's John King. "This is significant," the source said.

The Boston Globe is reporting the same thing.

The Globe offers more detail atop their home page, reporting that "Authorities have an image of a suspect carrying, and perhaps dropping, a black bag at the second bombing scene."

Update:  Ace notes that 4chan posters have put some images together that show a man with a black backpack, holding an object in the shape of a pressure cooker, standing amid the marathon spectators.

Update: CNN's John King says a suspect has been arrested. Suspect described as "dark-skinned male" says @JohnKingCNN, adding was given further description but won't inflame tensions by repeating.

Also on CNN, Fran Townsend reports that an individual has been arrested, based on evidence in two different images that authorities have been examining.

Update: Media confusion, as CNN and Fox report an arrest, NBC and CBS report no arrest has been made. Now CNN on air is walking things back a bit. It's the mainstream media and a developing story -- caution is always advised.

Update: The FBI is pushing back, insisting that no arrest has been made at all.