Internal Zimbabwean police documents passed to the Guardian suggest the army has been responsible for murder, rape and armed robbery during the ongoing brutal crackdown in the southern African country.

In more than a dozen investigation reports shared with the Guardian by police officials frustrated at the apparent impunity of the military, a series of alleged attacks are described, including two murders and the rape of a 15-year-old girl.

Police investigators wrote that all the acts were committed by men wearing army “uniforms” or “camouflage” – a style of wording allowing the police to avoid making direct accusations against the powerful military.

Officially, the Zimbabwe Republic police, the national police force, has blamed the violence on criminal “rogue elements” who have stolen army uniforms, and said the charges of widespread abuses by security and the armed forces have been fabricated. But in most cases described in the documents seen by the Guardian, the assailants carried automatic weapons, which few people other than soldiers and police possess.

Protesters stand behind a burning barricade during a protest on a road into Harare on 15 January. Photograph: Philimon Bulawayo/Reuters

At least 12 people are thought to have died when security forces opened fire on civilians during a three-day shutdown called by unions after a fuel price rise this month. One police officer is believed to have been killed. The death toll is expected to rise.

The violence is the worst in Zimbabwe for at least a decade and has dashed any remaining hopes that the end of the 37-year rule of the autocratic leader Robert Mugabe 14 months ago would lead to significant political reform.

The leak of the documents suggests increasing tensions between the military and people within civilian law enforcement agencies.

One report, filed by police in Glenview in the capital, Harare, on 14 January, describes how a Toyota driven by two men, including a 29-year-old named as Trymore Nachiwe, was blocked by a pickup truck without number plates or other identification. Men in civilian dress and some wearing Zimbabwe National Army uniforms then got out of the pickup armed with stones, iron bars, machetes and teargas canisters, the report says.

They smashed the Toyota’s windows and ordered Nachiwe and his friend to lie down by the roadside, where they were punched and kicked repeatedly. Nachiwe managed to reach his home but died in hospital after seeking medical attention the following day.

Another report details the murder – apparently by security forces – of Kudakwashe Rixon, a 22-year-old, who was seized by uniformed men at a bus terminal in central Harare on Sunday.

The report, filed at Harare Central police station on 27 January, said Rixon had been driven with others to a remote “bushy area” where they were beaten with wooden clubs, whips made with metal wire and iron rods. Rixon managed to get home, where relatives tried to care for him but he died on arrival at Harare hospital a day later.

A third report describes how a 15-year-old in the town of Chitungwiza, outside Harare, was forced into a park by three men wearing army camouflage and carrying rifles and made to lie on a concrete table where she was raped.

Emmerson Mnangagwa in Harare on 24 January. Photograph: Philimon Bulawayo/Reuters

Responding to earlier reports of violence, the country’s president, Emmerson Mnangagwa, promised that wrongdoers within the security forces would be held accountable. On Monday, he said he was “appalled” by a Sky News report showing security forces beating a handcuffed man.

The army has been responsible for a series of brutal crackdowns since Zimbabwe gained its independence in 1980, and played a key role in the ousting of Mugabe. Soldiers shot dead six civilians in Harare days after Mnangagwa won contested elections last year, and have deployed in strength in cities in recent weeks.

The reports also describe the alleged theft from homes and businesses of items including iPhones, computers, televisions, and even an electric iron. Twelve cans of beer were stolen in an attack on a bar.

Among dozens of reports of robbery are incidents in which groups of men wearing army uniforms and carrying automatic weapons arrived in unidentified vehicles, forced their way into homes through threats and then looted property worth up to $8,000.

In one incident, an eight-year-old was threatened with a handgun to force his parents to reveal their savings. In another, a man was stopped while walking home and beaten with whips. His wallet containing $235 was taken. In a shopping centre in Glenview, cash was taken from the till, along with telephones and drinks.

The documents – which apply only to Harare – do not give a comprehensive view of the extent of the violence associated with the crackdown, which took place across the country. Police were so stretched during the worst of the unrest and violence between 15 and 20 January that no or few reports were filed during this period.

Many crimes committed by security forces have not been reported to police because victims are often fearful of detention or further violence.

Courts are currently processing about 1,000 detainees, largely picked up in a series of sweeps by security forces through poor neighbourhoods in and around Harare, as well as other cities, since the unrest began.

Hundreds of activists, opposition politicians and civil society leaders are still in hiding. It now appears very unlikely that Mnangagwa will achieve his stated aim of ending Zimbabwe’s pariah status to unlock the massive financial aid necessary to avert total economic collapse.

This suggests basic commodities such as food, fuel and medicine will remain scarce and increasingly expensive, making further protests likely.

Authorities in Zimbabwe will face new pressure in coming days, as hundreds of thousands of civil servants prepare to strike after rejecting a government package to boost their income.

Courts are struggling to process the huge number of detainees, who are being kept in overcrowded cells and prisons. New “fast track” trials have involved up to 60 accused being represented by five lawyers appearing at courts to face charges that could lead to lengthy prison sentences. Seven people have now been charged with subversion, an unprecedented number.

On Tuesday hundreds of lawyers marched through Harare to protest against the continued deployment of the military and the new judicial procedures.

“Where people have committed crimes, please deal with them in accordance with the international law [and] follow due process,” Beatrice Mtetwa, a leading human rights lawyer, said.

Nelson Chamisa, the leader of the main opposition party, the Movement for Democratic Change, said the authorities were trying to divert blame from economic failings.