'Thankyou Ma'am' by Langston Hughes is the first one that comes to mind.

Ask the pupils (before they get to the real motive) why Roger tried to snatch the pocketbook. (Answer: to buy some blue suade shoes - cue song).  Then ask them to 'uncover the motive' and read the line where they found it.

Mr. Know All by William Somerset Maugham

http://tlc.cet.ac.il/ShowItem.aspx?ItemID=3504f07c-ac88-42a7-82b1-c911326bec86&lang=EN

Ask why Mrs Ramsay insists the pearls are fakes.  Pupils should identify the clues to back up their answer.

Tell weaker pupils that they have to be detectives.

If anyone has the materials or a link to an ELT murder mystery, you'd make my day!