Translation:He tells the story clearly and the police listen.
agus éisteann na póilíní" isn't a "while X is happening" ending - that would be "while the police are listening", and the Irish is agus na póilíní ag éisteacht*.
If the word after agus is a verb, then it's "and", if the word after agus is the object (a noun or a pronoun), then it can be translated as "while".
Because Garda isn't the Irish for "police".
If you check www.garda.ie, you will see
Is é An Garda Síochána an tSeirbhís Phóilíneachta Náisiúnta in Éirinn.
(An Garda Siochána is the National Police Service in Ireland) and
comhnascadh Póilíní Cathracha Bhaile Átha Cliath leis An Garda Síochána sa bhliain 1925 (the Dublin Metropolitan Police merged with the recently established An Garda Síochána in 1925)
The Irish for the Police Service of Northern Ireland is Seirbhís Póilíneachta Thuaisceart Éireann
If you cause trouble in Dublin Airport, you will be dealing with Póilíní an Aerfoirt, and if you join the Irish Army, you might have to deal with Póilíní Airm.
So every Garda is a policeman, but not every policeman is a Garda.
Thank you for the answer - I was thinking less of a person being part of the police, but my thinking was rather influenced by the fact that the police as a whole is viewed as a unit in German and hence "die Polizei" is a singular word there. Which I think is true for most mass nouns in German as opposed to English.