InputEventScreenTouch is the one you want. As you said, each event has pressed and released. Once its pressed that means touch is active and it is active. Once touch is removed event is fired with same index id with "pressed" variable false. That means touch was active until now.
if event is InputEventScreenTouch:
if event.pressed :
first_touch = event
# Touch is pressed from now on
if !event.pressed and event.index == first_touch.index:
first_touch = null
# first touch was just removed.