A jury has failed to reach a verdict on two men accused of being part of a cell that tried to set off suicide bombs on London's transport system on July 21, 2005.
Manfo Kwaku Asiedu and Adel Yahya were accused of conspiracy to murder in the failed attacks which took place a fortnight after suicide bombings killed 52 people in the UK's capital.
The trial had lasted almost six months and prosecutors must now decide whether to hold another trial with a new jury.
On Monday, four men - Muktah Said Ibrahim, Yassin Hassan Omar, Ramzi Mohammed and Hussein Osman - were found guilty of the same charge at Woolwich Crown Court in east London.
'Hoax' attempt
The four men, Muslims of African origin, had tried to set off homemade bombs on three underground trains and a bus but the explosives had failed to detonate.
They had claimed that the bombings were a hoax designed as a protest against the war in Iraq.
Asiedu, who admitted he had dumped a fifth bomb in a park in north London, broke ranks with his co-accused during the trial, saying the plot was genuine but he had been duped into taking part.
Yahya, who had left the country six weeks before the failed attacks, denied having any knowledge of the plot.