A little-reported public inquiry broke up on Thursday after weeks of harrowing allegations about how British troops murdered and tortured Iraqis after a fierce gun battle in 2004.

The al-Sweady inquiry, named after a 19-year-old Iraqi, and which has cost nearly £18m so far, will resume in the autumn when it is due to hear evidence from more than 200 British military witnesses.

It was forced on the Ministry of Defence in 2009 after high court judges accused it of "lamentable" behaviour and serious breaches of its duty of candour. The inquiry heard how the British military police were slow to investigate the allegations, and potentially significant forensic evidence related to the incident has still not been provided by the MoD.

Nine Iraqis say they were tortured after being taken to a detention centre at Shaibah base near Basra and held there for four months. They say they were taken, along with 20 murdered Iraqis, to a British base, Camp Abu Naji, after a fierce gunfight in what became known as the battle of Danny Boy, a British checkpoint near Majar al-Kabir, north of Basra, on 14 May 2004.

The battle, in which soldiers used their bayonets in close-quarter fighting, began when some 100 armed insurgents attacked a patrol from the Argyll and Sutherland Highlanders and the Princess of Wales's Royal Regiment.

The MoD and the army vigorously deny the allegations made by the Iraqi victims and their families. One unanswered question is why dead and wounded Iraqis were taken to the British base after the battle.

It has been suggested that the soldiers wanted to find out if any of the Iraqis had been responsible for the brutal killing, a year earlier, of six members of the Royal Military Police in Majar al-Kabir.

Iraqi witnesses have described to the inquiry "bodies distorted and mutilated, eyes missing, tongues cut out, and noses cut off". However, a British pathologist, Dr Peter Jerreat, told the inquiry this week he could see no evidence of torture or mutilation on photographs of seven of 20 Iraqis killed. Their injuries were in his opinion sustained before the men died, most likely on the battlefield.

Jerreat examined photographs and DVDs of the men as part of his investigations, and added that it was possible to give a valid opinion on the nature of injuries from photographs, but that it was difficult to give evidence on cause of death without being able to carry out an internal examination.

Some Iraqi witnesses came to London to give evidence. Forty others gave evidence via video link from Beirut.

They included the wife of one of the dead Iraqis, Bushra Sakher Katem. "Why did he die, for which reason? I beg you to look into this and get me an answer," she said.

The inquiry chairman, Sir Thayne Forbes, a former senior judge, told her: "Mrs Katem, you may be assured that I will give very careful consideration to all the evidence in this matter and I will endeavour to provide the answers to questions such as those that you have just raised".

The inquiry is due to end next February.