Saudi student Abdulrahman Ali Alharbi was detained for “acting suspiciously” at the Boston Marathon finish line on Monday but was later ruled out as a suspect by federal officials after they raided his apartment.

Officials said they were talking to Abdulrahman Ali Alharbi, 22, only as a witness.

Abdulrahman Ali Alharbi, who is studying English, is still in hospital after suffering from serious burns and is said to be cooperating fully with authorities. He was tackled to the ground by a civilian who believed he was acting suspiciously.

More than 24 hours after the deadly terrorist attack which killed three people and injured 183 at the Boston Marathon, authorities are no closer to finding out who is responsible and say the investigation is “still in its infancy”.

Saudi student Abdulrahman Ali Alharbi was detained for “acting suspiciously” at the Boston Marathon finish line on Monday but was later ruled out as a suspect

No one has claimed responsibility for the attack and authorities do not even know if it was a group or an individual, Al Qaeda or a sympathizer, a lone wolf or a right wing extremist group capitalizing on it being Patriot’s Day.

Speaking this afternoon at a press conference, the FBI agent in charge, Rick DesLauriers, said they have received more than 2,000 tips which they have looked into but the range of suspects still remains wide open.

He said authorities are working around the clock and forensic evidence has been sent to FBI labs in Virginia to be analyzed and reconstructed.

Rick DesLauriers also asked people to report anyone who talked about targeting Monday’s race or showed interest in explosives or if anyone was seen carrying a heavy nylon bag in the area at the time.

“Someone knows who did this,” he said.

“Co-operation from the community will play a crucial role in this investigation,” Rick DesLauriers added.

It was also revealed today that important clues are being collected from the victims themselves.

Doctors at Tufts Medical Center said they had removed countless pieces of shrapnel from injured bodies and were turning them over to police and federal agents.

Dozens of pellets and nails were collected and sent away as evidence. Some had as many as 40 fragments in their body.