Rafael Ramos and Wenjian Liu National Blue Alert Act

President Barack Obama and Vice President Joe Biden greet the families of slain Officers Ramos and Liu after the signing of the Rafael Ramos and Wenjian Liu National Blue Alert Act of 2015 in the Oval Office, May 19, 2015. The bill is to establish an alert system for police threats in the wake of the ambush killings of the two NYPD officers in Brooklyn, N.Y. (Official White House Photo by Pete Souza)

Featured in the Following Photo Galleries:

• May 2015: Photo of the Day