A full strace log will include all of the data that the process reads and writes, possibly in hex. ISTR that the default is to show only the first few bytes of each data transfer. Assuming that you know some specific sensitive data, try converting the first few bytes of it to hex and searching the log for that.
If you trace only a period of time, the log will (obviously) include only what happened during that time; similarly, you can trace the entire execution of the process and then edit the log file down to only the critical period. You can further restrict it, by command-line options, not to show reads and writes at all, but the result might not be useful at all for the developer.