Mr Mohammed was arrested in west London on 29 July along with Muktar Said Ibrahim. He is suspected of attempting to bomb the Tube near Oval station.
Few details are known about him and his name had not been released prior to his arrest.
Another man arrested at the same time is reported to be his brother, although this has not been confirmed by police.
That man is suspected of being a fifth potential bomber.
Muktar Said Ibrahim, 27
Muktar Said Ibrahim, also known as Muktar Mohammed Said, is suspected of trying to set off a bomb on a number 26 bus in Hackney.
He came to Britain from Eritrea in 1992, aged 14, as a child refugee and went to school in Edgware, north London.
He applied for British citizenship in 2003 and was naturalised in September 2004.
Mr Ibrahim was arrested in west London on 29 July, eight days after the attempted bombings.
Yasin Hassan Omar, 24
Yasin Hassan Omar arrived in Britain from his native Somalia in 1992 aged 11 and was granted exceptional leave to remain in Britain in May 2000.
He lived in a flat with Muktar Said Ibrahim in New Southgate, north London, where he received housing benefit.
Mr Omar is suspected of the failed attack on the Victoria Line between Oxford Circus and Warren Street.
He was arrested in Birmingham on 27 July, the first of the four suspects to be held.
Osman Hussain/Issac Hamdi, 27
Mr Hussain was arrested in Rome on 29 July and is suspected of trying to bomb a Hammersmith and City Line train at Shepherd’s Bush.
He was born in Ethiopia but became a British citizen and he has also been named as Issac Hamdi.
He was tracked to Rome via his mobile phone, from where Uk police luanched extradition proceedings.
He is believed to have left London on 26 July and travelled on a Eurostar train via Paris, Milan and Bologna, before reaching Rome.