This is report explaining that DEA was aided by NSA's surveillance system at the time they were persecuting a wanted criminal Gonzalo Hinojosa while he had been in Panama by using data obtained by NSA's systems. The report suggests this person was very evasive and dangerous perhaps this is why DEA collaborated with NSA.
Another example of LE and NSA cooperation.
Shouldn't NSA be concerned only about foreing intelligence without doing anything related to LE? If there is a reason for such cooperation to exist, how far can cooperation between a LE organization go with an intelligence agency of the same country? And what type of criminal actions substantiate to do this? Terrorism, child abuse, et cetera.
For example, if FBi wanted to research more about a wanted person inside another country out of their reach, may it use NSA's systems to track down this person's movement with cellular networking? Or spy on his Internet activity with surveillance systems mentioned?