Hard
Shared rows and columns
Two suspects locked into the same two rows claim both.
Sometimes two suspects are each limited to the same two rows. You cannot say which is where, but between them they fill both rows, so everyone else is out of those two rows.
The idea scales: three suspects confined to the same three columns claim all three. Hard cases hide one of these, usually after the easy crossings are done. When you feel stuck, list each remaining suspect's rows and look for a pair that matches.
How to spot a pair
For each suspect not yet placed, write down the rows they can still reach. Look for two suspects who between them can only reach the same two rows. They will fill those two rows, one each, so cross both rows out for everyone else. Then do the same with columns.
The pair does not tell you who goes where. It only clears the two rows for the others. The order usually falls out a few moves later, from a column or one of their clues.
Triples
Three suspects who together reach only three rows claim all three. Each of them need not reach every one of those rows: one might have rows one and three, another three and five, the third one and five. Triples are harder to see, so when a Hard case stalls, list the rows on paper.
When to look for it
Look for subsets once the easy crossings stop working. A Hard case usually hides one in the middle of the solve, and finding it opens the rest of the board. If no pair turns up in the rows, try the columns, where the same pattern often hides.
The diagram, step by step
On the 5×5 board above, Clara and Oscar can each only be in rows two and four. Those two rows now belong to them. Paula had cells in both rows, so she loses them and keeps only her cell in the top row, which places her.
Practice case: Hard 7×7
This case needs the technique above. Try it before you read the next tip.
The victim. She was alone with the killer. She was on a deckchair.
Pick a suspect, then tap a cell.
Play this case and the whole casebook in the app, free on iPhone, iPad and Android.
