Three unidentified men or women masterminded the forgery of postal votes for Labour candidates in Aston during last year's Birmingham City Council elections, a court was told.
The efforts of the trio, referred to only as Mystery A, B and C, were uncovered by a handwriting expert who found conclusive evidence of matching handwriting on scores of ballot papers.
An election court, which is considering a petition to have the three winning Labour candidates in Aston thrown out of office and fresh elections held, heard that the forgers used a variety of false signatures and addresses to fraudulently complete declarations of identity and application forms for postal votes.
All of the votes examined were for Labour and none were for the other candidates standing in the election.
Ravi Sukul, representing the petitioners, said Mystery A had filled in 162 declarations of identity. The names and addresses were different, but the handwriting was the same in each case.
The forger used 34 different witness signatures in an attempt to cover his tracks.
Aston Labour councillor Mohammed Islam was most likely to have been the Mystery B forger, according to the petitioners.
Coun Islam, who gave evidence to the court last week, denies any wrongdoing.
Mr Sukul said the handwriting expert had compared an example of Coun Islam's genuine signature with those found on forged declaration of identity forms.
There was conclusive evidence that the signatures on the ballot forms matched that of Coun Islam in 122 cases.
Such examples of matching signatures could not have occurred by coincidence, Mr Sukul added.
Mystery C forged about 50 declarations of identity, under the alias Muhammed Anwar Ali, and used several different addresses.
The petitioners claim more than 1,000 Aston postal votes were forged to favour Labour candidates.
A pre-trial scrutiny of 745 suspicious ballot papers found that 675 were marked with crosses for Labour.
Jerry Hayes, representing two of the Aston Labour councillors, produced evidence from the same handwriting expert to suggest that the Liberal Democrats had also been responsible for forging postal votes.
There was strong evidence to implicate losing Lib Dem candidate Ayoub Khan in improperly witnessing declarations of identity, Mr Hayes claimed. Mr Khan denies any wrongdoing.
The election court, which is sitting at the Birmingham and Midland Institute in Margaret Street, is expected to hear closing submissions in both the Aston and Bordesley Green petitions next week.
Deputy High Court judge Richard Mawrey QC, who is sitting as elections commissioner, will deliver his judgement at a later date.