opinion:

If something goes wrong is the 1st response to investigate

Or

Jump on IM and ask the person who last committed?

I would be in the opinion to have a look yourself and try identify the problem before fucking ranting at the last person who touched the code,

Reasons, Maybe that last person is busy and doesnt want to context switch back for a simple problem that would take less than 5 mins fucking investigation time, 1st thing in the morning too doesnt help!