Some 30 arrests have been made as a result of the bombing in Meskel Square on 23 June that killed three people and injured over 150.
Among those held are the deputy police commissioner of Addis Ababa and several other high ranking police officers on grounds of the lapse in security.
The bomb exploded close to where the prime minister Abiy Ahmed was addressing a large crowd, one of the largest in recent history, who had come to hear him speak about his new reform measures and a peace deal with Eritrea.
The prime minister has said that the United States, its key western ally, will be sending FBI agents to help investigate the bombing, but this has not yet been confirmed by the US embassy in Addis Ababa.
The prime minister only took office in April after a considerable period of tension and unrest in Ethiopia but he has wasted no time outlining his reforms and policies.
He has lifted the emergency measures that were in force when he took office, released thousands of imprisoned dissidents, loosened media restrictions and allowed social media to operate.
He has been reaching out to neighbouring countries, in particular Egypt and Sudan, to reassure them of Ethiopia’s goodwill. He has secured much-needed financing from the United Arab Emirates and has announced several important infrastructure projects to secure Ethiopia’s opening to the sea, as well as a plan to rebuild the navy. He would also like to see a partial sell-off of some state controlled assets, such as telecoms and Ethiopian Airlines.
One of the most controversial issues is a call for the normalisation of relations and reconciliation with Ethiopia's long-time enemy Eritrea. This will mean the official recognition of Eritrea’s claim to the border town of Badme.
Another has been the prime minister’s declared policy to reform the military and security services. These, along with the some of the country’s key financial and economic assets, have been dominated for decades by the Tigray from the north of the country, on the border with Eritrea. Ahmed is from the majority Oromo, who along with the Amhara, have played second place to the much smaller Tigray who amount to only six per cent of the population.