MR Simon McCrum asks that the Government consider re-introducing capital punishment to show that it is tackling the recent wave of violent crime with all the resources at its disposal (South China Morning Post, January 9). He believes that this would deter mainland gangs from armed robbery in Hongkong. This ''strong belief'' in the deterrent effect of the death penalty should be moderated by persistent evidence that it is not effective in reducing violent crime. Statistical evidence from New York State shows the opposite: that murders increased in the months following an execution. Mainland gangs are doubtless tempted to Hongkong by the potential prizes rather than the possible penalties. There are many other arguments against the death penalty which I would be pleased to put to Mr McCrum or other readers who may contact Amnesty International on 3001250. CHRISTOPHER HOMFRAY New Territories