A 21-year-old man was arrested in the fatal stabbings of two people on New York City subway trains, police said.

Rigoberto Lopez, from Brooklyn, was taken into custody on Saturday night and was formally arrested on Sunday on charges of murder and attempted murder, police said.

One of the victims was discovered dead on a train in Queens late Friday with several stab wounds to his neck and torso, police said.

Two hours later, a 44-year-old woman was found stabbed to death in a subway car in upper Manhattan.

Two non-fatal attacks, one involving a 67-year-old man and the other involving a 43-year-old man, also occurred in upper Manhattan.

Authorities believe all four victims were homeless.

Police said they believe Lopez may have committed all of the attacks.

Police leaders said they would deploy an additional 500 officers into the subway system to guard against future assaults.

“To the victims, to the victims’ families, we are 100% committed to getting justice … to bring closure to the families of this terrible incident,” NYPD Commissioner Dermot Shea said.