The Police Ombudsman is facing calls to investigate why Martin McGuinness was not interviewed about Bloody Sunday.
In his report into the 1972 killings by British soldiers in Derry Lord Saville said Mr McGuinness was "probably" carrying a Thompson sub-machine gun on the day. Mr McGuinness denies this.
DUP East Derry MP Gregory Campbell lodged a complaint on the police's failure to question the Deputy First Minister.
He said: "I have now been left with no option but to write to the Policing Ombudsman with a formal complaint against the police in not carrying out what most people would regard as their impartial duty to question an identified person who has admitted being a senior member of the Provisional IRA at a time when that organisation was engaged in killing people in the vicinity where two police officers were also murdered.
"If the Saville Report has led to soldiers being questioned about their actions at that time then that same report which indicated that Mr McGuinness 'probably' had a sub machine gun must lead to his being questioned about knowledge which he may have also."