Sewage Backup- Due to City Issue

[Mak K.]

So my tenant says that there was a maintenance being done at the ditch (adjascent) behind the house a day before the two toilets & bathtub got sewage backup. It was gross and water was everywhere from master room, closet and living room. Currently I am working on getting it fixed.

But I would like to know how do i got about investigating if it was something cause by city maintenance issue? How do I investigate. Who do I call to get log book of what they did in my neighborhood. Do I need a lawyer (Contingency basis?)

Anybody had experience in fighting with city when they messed up? How do I prove it is city's fault? I would like to investigate if it was really city's fault?