HRW said Hamas' failure or refusal to investigate the deaths "makes a mockery" of its claim that it is upholding the law in Gaza, the BBC reported Thursday.
"Hamas' inability or unwillingness to investigate the brazen murders of seven men makes a mockery of its claims that it's upholding the rule of law in Gaza," Sarah Leah Whitson, HRW's Middle East director said. "Even before the killings, the abuses the men suffered made the criminal justice system a travesty, regardless of their guilt or innocence."
The men were shot in public and one body was dragged through the streets by a motorcycle in November during an eight-day conflict between Hamas and Israel.
HRW said Hamas leaders also failed to begin a promised inquiry into the deaths, a claim Hamas denied.
On Thursday, Hamas spokesman Ihab al-Ghusain said an inquiry led by the prosecutor general was set up soon after the incident and has made recommendations to the Cabinet.
The men were convicted by a military court in Gaza of spying for Israel, but HRW said the convictions may have been based on evidence gained by torture.
The HRW report was issued Thursday, the final day Hamas said suspected collaborators with Israel could surrender with the promise of amnesty, the BBC said.
Meanwhile, Israel's Shin Bet internal security service said it found dramatic rise in the number of attempts to kidnap Israeli soldiers in the West Bank, Yedioth Ahronoth reported Friday.
Shin Bet said 33 kidnapping attempts have been foiled since the beginning of 2013, compared with 24 thwarted attempts for all of 2012.
Senior officials told Yedioth Ahronoth the prisoner exchange deal which secured the release of Israeli soldier Gilad Shalit encouraged Hamas to attempt additional kidnappings.
"We detect within Hamas the desire and capability needed for these kidnappings, as well as a lot of audacity," an official said. "So far we have been able to thwart the kidnapping attempts, but the scope is extraordinary, and it is clear we will not be able to foil these attempts forever."