This is the 115th most frequent Swedish word.
sista
"Last" or "final."
Here, 'sista' is used as an adjective to denote the final item in a sequence of buses.
Den sista bussen går klockan tio.
The last bus departs at ten o'clock.
In this case, 'sista' describes the final occurrence of an event, namely the act of seeing.
Sista gången jag såg honom var förra året.
The last time I saw him was last year.
In this sentence, 'sista' modifies 'försök,' meaning that it was the final attempt made.