Its easier with three detectors mounted on the radius of a circle,the first detector to be triggered starts two timers to time the delay to the other detectors,the delay can be seen as two circles centred at the two detectors they expand at a velocity of c and where they meet is the solution to two simult equations,which one is your answer depends on which detector triggered first. Its not quite the full answer but its near enough.You then need to rotate axis and stuff.