One of the things that I find frustrating in screeps is that you cant directly tell which tower shot which creep or which creep targeted which other creep.
I recently discovered that this information is stored in the database in the actionLog object that is attached to most room.objects. It contains information about whether a creep or tower has attacked, repaired, rangedAttacked etc and which location it attacked / repaired... as well as whether that object has been attacked.
I would request the action log is added to the API for creeps and structures. As this information is already in the database I would of thought it would be a fairly simple addition that would have minimal impact on performance.