The bodies of bomb attack victims are covered with banners and flags as Turkish riot police secure the area near the main train station in Turkey's capital Ankara, on October 10, 2015
Istanbul (AFP) - Two weeks after more than a hundred people were killed in an Ankara bomb attack, Turkey is still unravelling clues that suggest the Islamic State group was responsible, fuelling opposition anger over an apparently enormous security lapse by the government.
IS was immediately considered "suspect number one" after twin suicide bombings on October 10 in front of the city's train station killed 102 people, due to similarities with an earlier bombing blamed on the jihadist organisation.
Once again, TNT explosives packed with metal ball bearings devastated a pro-Kurdish rally: Ankara seemed a more ambitious version of the bombing in Suruc on the Syrian border in July, which left 34 people dead -- and critics say the security forces should have seen it coming.
Media reports this week said the national police headquarters had warned in September that IS militants were preparing a large attack in Turkey, such as hijacking a plane or detonating suicide bombs in a crowded location.
The post-attack probe focused on some 20 known jihadists and uncovered 11 suicide vests, six Kalashnikovs, 22 hand grenades and explosives, suggesting there were plans in place for another attack on Turkish soil.
According to the pro-government news agency Anatolia, the cell had originally planned to attack the headquarters of the pro-Kurdish and liberal Peoples' Democratic Party (HDP), but targeted the peace rally at the last moment.
Prosecutors this week formally identified one of the suicide bombers, Yunus Emre Alagoz, a young Turk from the Islamist militant stronghold of Adiyaman and the brother of the man suspected of carrying out the Suruc attack.
Turkish media have identified the second bomber as Omer Deniz Dundar, who had twice been to Syria -- and was on a list of dangerous individuals -- though some reports say the accomplice may have been a foreign IS member.
- 'Protecting IS' -
Police are reported to have arrested one of the men who helped get the two bombers to their targets, who allegedly told investigators he was amazed they had all got through a checkpoint unnoticed.
Turkish daily Today's Zaman claimed the arrested man, named Yakup Sahin, had been tailed by security forces on suspicion of ties with IS, but police lost him and failed to react when he surfaced again in Ankara on the morning of the attack.
Amid the confusion, President Recep Tayyip Erdogan on Thursday pinned responsibility for the Ankara bombing on a "terror collective" comprising not only IS, but also Turkish and Syrian Kurds and the Syrian intelligence service.
Ankara's chief of police and two other officials were fired in the wake of the attack as details emerged of failures by security services to keep track of suspect individuals, with the government accused of seriously underestimating IS.
As snap elections on November 1 near, the opposition is increasing putting pressure on the government to admit security failings -- particularly considering that the father of the presumed second bomber had told police to arrest his son and lock him up.
Critics have accused the state of encouraging violence against the HDP -- which presents the biggest challenge to the government at the elections -- and going soft on IS, enemy of Turkey's enemies, the Syrian regime and the Kurds.
Kemal Kilicdaroglu, head of the social-democratic Republican People's Party (CHP), insisted recently that the state's failure to dismantle jihadist networks could mean just one thing: "I will say it clearly, it is about protecting IS".
While Davutoglu has brushed off the allegations, prosecutors have nonetheless opened a preliminary investigation into the country's interior minister, Selami Altinok, on the grounds of negligence, the Hurriyet newspaper reported Friday.
They may not get very far: a green light from the government is needed to strip minister Selami Altinok of his political immunity and launch a full investigation -- and both Davutoglu and Erdogan have refused to hand over their man.