Suou's deduction process is always nice to see

Suou is going through her usual deduction process and it's quite interesting to see how she's trying to piece together the mystery. Everything seems to go around the figure of Shion Basquiat that was buried near the school in an inconspicuous place.
Suou wondered if he was the adoptive father who took in Dalia at young age, but from the records of the school no other Basquiat was present at the school at anytime aside from Dalia herself.
So who was he? Why is he buried near the school? And why is there an angraecum flower right next to it? it's technically a special flower according to Suou in the school, the only one that is maintained by the teachers and not by the students and it means "prayer".
Also are we sure it's someone older than Dalia or maybe someone around her age? Suou didn't mention the dates present (if any) on the tomb.
I guess the next step is to try and ask Dalia in a roundabout way about it as she's the only one who may know something about it.