Investigators are looking for two men that are persons of interest in Monday's Boston Marathon terror attack and have distributed photos for “law enforcement eyes only.”

According to FOX News, The FBI is not sharing the photos with the public, but those who have seen the photos called them “clear.”

In the photos,

One of the men has a backpack that appears to match the bag believed to have been used in the attack. The other man also appears to have a bag of some kind.

A federal law enforcement official asked that the images not be made public for fear of jeopardizing the investigation.