Why does it look suspocious that oen brother has his arm in a sling??

The lawyer, Levi Bell, manages to get all three men to write a line for him. He pulls out some old letters and examines the handwriting, only to discover that none of three men had written the letters to Peter Wilks. The real Harvey Wilks explains that his brother had transcribed all his letters because his handwriting is so poor. Unfortunately, since his brother has a broken arm, he cannot write and therefore they cannot prove their case. It would seem rather the "brother" who could prove his authenticity happens to be in a sling.