A scientist who gave evidence for the defence in the 21 July bomb plot trial believed he had a "civil duty" to be an expert in the case, a court has heard.
The six deny charges of conspiracy to murder
Hans Michels, a professor of safety engineering at Imperial College London, "wanted justice to take place", Woolwich Crown Court was told.
His words were summarised in closing submissions by George Carter-Stephenson QC on behalf of Muktar Said Ibrahim.
He and five other men deny attacking London's transport network in 2005.
'No expense spared'
In his closing comments, Mr Carter-Stephenson said the professor was "not a man who actually wanted to be involved as an expert in the case".
"And you may think that is not surprising, bearing in mind the sort of workload he had," he added.
Mr Michels has been involved in investigations into the Ladbroke Grove train crash and the Buncefield oil depot blast, the jury heard.
Mr Carter-Stephenson continued: "Why did the professor become involved?
He then quoted the professor as saying: "I thought that, having been paid by the state, I had a civil duty to do it. I agreed because I wanted justice to take place."
Mr Carter-Stephenson told the court the professor was "a man who clearly believed that justice required the defence had the services of an expert too".
Mr Carter-Stephenson told the court that "no expense has been spared" in the presentation of the prosecution case, particularly in relation to tests conducted at the Forensic Explosives Laboratory at Fort Halstead, Kent.
Mr Michels, who was instructed on behalf of Mr Ibrahim, funded his own experiments, he said.
Mr Ibrahim, 29, of Stoke Newington, north London, is one of six men who deny conspiracy to murder.
The others are Ramzi Mohammed, 25, of North Kensington, west London; Hussain Osman, 28, of no fixed address; Yassin Omar, 26, from New Southgate, north London; Adel Yahya, 24, of Tottenham, north London; and Manfo Kwaku Asiedu, 34, of no fixed address.
A further charge of conspiracy to cause explosions likely to endanger life, previously faced by each man, has now being left off the indictment.