British police revealed on Sunday that all 22 suspects arrested on suspicion of being connected to the heinous May 22 Manchester Arena bombing have been released without charges.

Over the days and weeks following the cowardly attack — which targeted an Ariana Grande concert and left 22 dead and 59 injured, many of whom were children — British authorities arrested a total of 22 suspects they believed may have been connected to the radical Islamist suicide bomber, Salman Abedi, a British citizen of Libyan descent. In response to the attack, police conducted a series of raids, including in the Manchester area, where Abedi's older brother was arrested.

Despite rounding up nearly two dozen suspects, British officials announced on Sunday that not a single one had been charged. They also revealed that they still do not know if Abedi acted alone or as part of a terror network. AP reports:

Russ Jackson, head of counterterrorism policing for northwest England, said police believe Abedi assembled the bomb himself, but it's unclear "whether he acted alone in obtaining the materials for the device ... and whether others knew or were complicit in the storage of materials knowing what was being planned."

Jackson said some of those arrested had offered "accounts which explain innocent contact with Abedi." He said risk to the public had been considered before suspects were released.

British police can detain a terror suspect for up to a total of 14 days without charges before the law requires their release.

Jackson indicated that despite concentrating law enforcement and intelligence resources for weeks to tracking Abedi's actions leading up to the attack and his possible connections, so far they are coming up empty. Law enforcement, he said, would continue to "work to understand the full extent of the involvement of anyone else."

In the days following the attack, Abedi's older and younger brothers and his father were arrested on suspicion of connections to terrorism. His older brother, Ismail, was arrested by British authorities the day after the attack but released last week without charges. His younger brother and father, Hesham and Ramadan, were arrested by Libyan authorities later that week; their current status in Libya, the Abedi's home country, is unclear.

ISIS has claimed credit for the attack, celebrating Abedi as a "caliphate soldier." Read more about Salman Abedi here.