Father Michael Canny said no cause could justify the “senseless” taking of life.
“What has happened has brought devastation to family and friends,” said the well-respected Derry priest.
“Here we find people who are judge, jurors and executioners, there’s no room for this in a civilised society.
“If anybody has any information about this murder they need to contact either the PSNI or Garda immediately. ”
SDLP MLA Pat Ramsey said he knows the Allen family well and hit out at the killers.
“One can only imagine what his mother and father are going through,” he said.
“There are no excuses for this most violent act. Shame on those who carried out this deed. Our community has suffered enough.
“Nothing will be achieved by this action last night.
“We need to have a community response to these attacks,” he said.
Mr Allen, who had two children, was fatally wounded in an attack at 9.20pm on Thursday. He died at the scene an hour later.