Theoretically, Chris Theodorakis's possible motive in the the Sam Westing murder is to get the money he needs for treatment for his unidentified illness. Chris had been "a perfectly normal kid" until about four years ago. He started "to get clumsy, just little things at first", but the illness progressed until now, he is confined to a wheelchair, unable to control the severe spasms which wrack his body. Chris, who has a special interest in ornithology, is intelligent and good-natured, completely in touch with what is going on around him, which makes his physical handicap that much more difficult to accept. There is apparently an experimental operation available that might help him, but it is very expensive.
Despite the fact that he does have a motive to want Sam Westing's inheritance, it is highly unlikely that Chris is the murderer. Chris does not dwell on his physical limitations, and in more than a few instances, it is pointed out that his interest in the Westing Game is based on his delight in being "part of the outside world". He guards his clues and insights into the case carefully, doling them out sparingly to his partner, Denton Deere, so that the doctor will have to interact with him as long as possible. Chris had never "asked for charity...all he wanted was to play the game".