Power everywhere after turning off the main circuit breaker
It's possible the panel you have illustrated is one of several such panels serving power into the unit, so you may need to do an exhaustive search for any others. 

It complicates things if this building has more than one unit.   Wiring to the other units could be still energized obviously... And this could create false readings on test equipment (capacitive coupling) -- or there could be actual cross-connection between the units, so your unit might not be fully de-energized unless others are too.

Cross-connection could be a load in your unit served out of their circuit... Or even a neutral cross, where their load is served from their panel, but it uses the neutral on your panel, and if you sever that neutral wire which has current flowing through it, the upstream side will be energized to 230V.  



A lot of testers are complete junk, or are not made for house wiring and need some skill to successfully apply.  

A common night light is surprisingly useful.   It is simple, honest and  not particularly reliable, which means you must check and double-check it. I honestly find them more useful than 3-lamp testers, though those are OK for a final check for new outlets.  

Plain old analog voltmeters with the moving needle are useful. 

Digital voltmeters (DVM) are useful but a little tricky.  They are so sensitive they can pick up micro-currents from capacitive coupling, which happens when a dead wire runs physically parallel to a still-energized wire. So you have a DVM a reading of 109 volts on a 120V circuit that you thought was turned off - plug a night-light in, and the voltage mysteriously disappears.

If the electricity is powerful enough to illuminate any light, even an indicator light -- that's not capacitive coupling, that's genuine power.