The Institute of Engineers of Rwanda has announced that it will carry out a parallel investigation into causes that led to the collapse of a four storey building under construction in Nyagatare District. This will be a second team after the Rwanda Housing Authority (RHA) announced a nine-man team to establish the cause of the tragedy on May 14.    Fred Rwihunda, the president of the Institute of Engineers of Rwanda told The New Times that preliminary findings indicate that stones that were used in the concrete were very weak."They were crushing them manually yet stones are very important in the concrete. Cement and sand are another story, but stones have to be the strongest,” he said.Rwihunda said they are still trying to assess the other details, like the iron bars used which he also suggests, were not of quality standard.The team will investigate probable causes of the collapse from three perspectives- poor quality materials, bad study, or bad execution."Any of the three can affect an entire project,” he told The New Times yesterday.Classification of engineers Rwihunda said that engineers in Rwanda are classified in five categories. The first one, the category of Fellows is still vacant, and will be made of people who are commended for exceptional contribution in their career, those who performed excellently not only the engineers, but also the other fields.The second category is made of corporate engineers. It currently has 120 registered members while 180 graduate engineers are also members of the Institute of Engineers in the 3rd category.  Intern engineers make up the fourth category and technicians with a diploma in engineering and those with secondary school certificates make up the 5th category.