Translation:We are pursuing the criminals.
The plural suffix is always optional in Klingon -- tlhIngan can thus be "a Klingon, the Klingon, Klingons, the Klingons". tlhInganpu' can only be plural: "Klingons, the Klingons".
It's never wrong to add the plural suffix, though, even when the verb prefix shows that the subject and/or object must be plural.
So you could equally correctly say HeSwI'pu' DItlha'lI'.
True in Welsh at least for numbers -- which is also where I personally tend to drop the Klingon plural suffix most often.
wej paq = tri llyfr = üç kitap = három könyv = "three book"
wej paqmey "three books" would also work, though, unlike Turkish or Hungarian. (But a bit like Welsh optionally, especially with higher numbers: tri o lyfrau.)
But: "how many books?" can only be paq 'ar?, not *paqmey 'ar?.
-taH does not preclude an action with a natural conclusion, though.
For example, paqvam vIlaDtaH is fine for "I am reading this book", even though reading a particular book has a natural conclusion (when you've reached the last page).
You can also -- but do not have to -- say paqvam vIlaDlI', which is more specific about making progress to a known goal.