The MDC Alliance claims 11 civilians died when the military opened fire on party supporters who were protesting the outcome of the July 30 elections early this month.
The main opposition said this in a Thursday statement which poured scorn on President Emmerson Mnangagwa's Commission of Inquiry into the widely condemned killings.
Police claim six civilians died as a result of the incident while the opposition's figure has not been confirmed by authorities.
The Nelson Chamisa led party said Mnangagwa's probe team was unbalanced as it comprised some individuals with known links to the President.
"Following the actions of the military on the 1st of August 2018 and the days that followed, which included leaving up to 11 people dead and a dozen others injured, a full, impartial and complete investigation of this case is a necessity," said MDC.
"It must be remembered that hundreds were displaced, arrested and abused, due to the uncouth military action."
The main opposition insists the probe was tailored at benefitting President Mnangagwa's ruling party and did not look set to incriminate its principal whose government is fingered in the killings.
Mnangagwa's seven member Commission comprises former South African President Kgalema Motlanthe, its chair, as well as former Commonwealth secretary general Emeka Anyauko, a Nigerian.
Top British attorney Rodney Dixon and Tanzania's former military boss Davis Mwamunyange complete its foreign component.
Locals include Univeristy of Zimbabwe professors Lovemore Madhuku and Charity Manyeruke with former Law Society of Zimbabwe president Vimbai Nyemba being the last member.
The opposition insists there was little by way of objectivity that could emerge from among Zimbabweans in the list.
"Charity Manyeruke is a well know Zanu PF cheerleader. The evidence is all over the public domain.
"Lovemore Madhuku is an interested party as he was a presidential candidate and has already made comments detrimental to the MDC Alliance. He is not a neutral by-stander," says MDC.
The opposition further insists Nyemba was not best suited for the probe team which could incriminate the State leader.
"Vimbai Nyemba is a Mnangagwa favourite," said MDC.
"She has already been appointed as chairperson of the Procurement Regulatory Authority and is also a member of another Commission of Inquiry into the sale of State land. Is there shortage of suitable persons that one person has to hog multiple positions."
MDC insists the three were pawns sent to perform a cover up job for Mnangagwa who has been up for wide condemnation over the killings.
It also says the setting up of the probe team was a Mnangagwa witch-hunt on opponents.
"The terms of reference are designed as a witch-hunt against perceived political threats and any credible opposition to ED (Mnangagwa)'s illegitimacy.
"Everything points to a clear effort to pin blame on key figures in the opposition as a way to weaken opposition thereby threatening democracy in Zimbabwe," said the MDC Alliance.