Identifying the perpetrators of the bombing on November 13 in Istanbul, which killed six people, is an important step towards accountability. US law enforcement has the capacity to assist.
The FBI can get involved when there is a US nexus — US victims or perpetrators — or when the crime involves a US citizen or US infrastructure (e.g. banking, etc.). Despite unsubstantiated allegations by Interior Minister Süleyman Soylu, there is no suggestion of a US connection to the attack on August 13.
When Turkey’s law enforcement or security/intelligence services request assistance through the FBI’s Legal Attaché at US Embassy/Ankara, cooperation would start immediately. Such collaboration would probably be discreet without much public attention.
If the Turkish authorities do not initiate cooperation, the US government can “strongly” recommend that the FBI works with the Turkish side. This would require a political push from the US administration or Congress. The FBI will not act on its own to recommend such collaboration.
Whenever there is a terrorist event like the bombing on December 13, the US Intelligence Community (including the FBI) closely monitors the situation to understand and learn about those involved. However, engaging US law enforcement is unlikely if Ankara has already decided to blame the PKK and launch reprisals.
Recent interrogations suggest that the Free Syrian Army, a jihadist group allied with Turkey, is more likely than the PKK to have played a role.