By Donatella Rovera, Special to CNN

Editor’s note: Donatella Rovera is Amnesty International’s senior crisis response adviser from Aleppo. The views expressed are her own.

Aleppo’s Kweik river, keeps washing up the bodies of men and boys who have been shot in the head at close range. Some have their hands tied behind their backs, some have marks suggesting torture.

Virtually every day this past week I have been getting early morning phone calls informing me of more bodies in the river – two on Sunday, four on Monday, seven on Tuesday, three on Wednesday…

All eventually float to the same spot in the Bustan al-Qasr district of Aleppo, Syria’s largest city, under the control of opposition forces but just a few hundred meters downstream from an area held by government troops.

It is too dangerous to try to recover the bodies at the point where they first appear – it’s too close to the government-controlled zone and right in the line of their sniper fire. Instead, local volunteers wait for the bodies to float another 300 meters or so downstream where they can be retrieved more safely.

On March 3, I arrived just as two corpses had been recovered from the river. On the face of one, something had been written with a blue marker. I had to look closely because the writing was pale and partially erased by the water and mud – the body was floating face-down when it was found.

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On the forehead was written “al-Assad ” and on the left cheek “Surya;” the writing on the right check and the chin could not be deciphered. People thought the two illegible words might have been “u bas” – as in the pro-regime refrain: “al-Assad, Surya, u bas” ([President] al-Assad, Syria and that’s it).

This man was Ahmad Ali Salah Hamwi. The following day his 12-year-old son Hassan was found with three other bodies in the river. They, like most others, were buried as “unknown” – there is no mortuary in the area, and in any case no electricity for a mortuary fridge.

Ahmad and his son were eventually identified on March 5 by relatives who went to a small office where local volunteers keep photos of all the bodies found in the river.

Every time I visited the office I found relatives of missing people looking through the gruesome collection of photos of bodies on one of the volunteers’ laptop. Since January 29, when 82 bodies were found, the river has delivered some 60 more corpses to the same spot. Some, but not all, have been identified.

Among those found on January 29 was a 15 year-old boy, ‘Abd al-Majid Reem Batsh, and his 38-year-old uncle Majid Nunu.

“’Abd al-Majid lived with his grandmother because his parents are working in Libya, “ one of their relatives told me. “On Sunday he went with his uncle Majid to go to register the birth of Majid’s new baby. They never returned home and on Tuesday their bodies were found in the river. The boy had torture marks on his face and had been shot in the heart; his uncle had been shot in the head.”

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Mohammad Shaaban Mustafa, a 47-year-old railway worker, left his home in Bustan al-Qasr on the morning of February 13 and went as usual to work in the Baghdad Station area (under government control). He never returned home. His body washed up the following morning with a large gunshot wound in the head.

Many of the victims were residents of the Bustan al-Qasr district or other areas under opposition control, who disappeared when they went into government controlled areas. Several families I met said their relatives were not involved in politics – so their crime may have been simply to live in an opposition-controlled area.

But government forces are not the only ones to commit such crimes.

In the Bustan al-Qasr district I also heard about Mohammad ‘Abd al-Jalil Khaled (aka Abu al-‘Abed), a 42-year-old father of two young children who was abducted by one of the armed opposition groups operating in the area and who died in their custody 10 days later. He was taken from his office at the beginning of October by members of the al-‘Amran/Martyr Nimr Battalion, belonging to the Afadi al-Rasoul Brigade.

The brigade initially denied holding him, but eventually allowed his parents to visit him on October 9; the visit took place in the presence of members of the brigade and therefore he could not speak freely.

The following Saturday his family learned that he was dead, and when they went to ask at the brigade they were told that Mohammad had been buried but were not told where. No explanation was provided as to the cause of his death.

After two weeks, Mohammad’s family was allowed to bury him.

Members of the brigade, armed and with an anti-aircraft machine gun mounted on a pick-up truck, brought Mohammad’s body, covered in mud, to his family at 6.30 one morning. They had to bury him immediately and were denied any of the funeral rituals such as washing the body, prayers at the mosque or a funeral procession.

To date, no one has been brought to justice in the case. When judges in one of the two legal committees that act as courts in the opposition-held areas of Aleppo summoned the brigade commander he turned up with a group of heavily armed fighters and seemingly managed to intimidate them into silence.

Another shocking case, on March 2, was the killing of Abdallah al-Yassine, a young media activist who had worked with many foreign journalists as a fixer/translator. I found his body outside one of the small hospitals in an opposition controlled area of Aleppo. He had been shot in the back of the head at close range.

The alleged killer of Abdallah al-Yassine is said to be the leader of one of the many armed opposition groups operating in Aleppo. He has reportedly been detained by the Jabhat al-Nusra brigade – believed to be the most powerful group among the opposition forces in the city – but further details have yet to emerge.

The longer this conflict goes on, the more complex, polarized and intractable it becomes and, as is so often the case, it is civilians who are bearing the brunt.