On that day police action against peaceful demonstrators at Pearl Roundabout left two protesters dead and more than a hundred injured.
Video footage from the day shows people being fired on with birdshot at point blank range. The footage was supplied by activists.
His brother told the BBC Mr Ghanami witnessed dead and wounded being taken to nearby Salmaniya hospital.
“He was very emotional. He stood in front of people in his uniform and said I cannot work for a killer institution.”
He told the crowd he was leaving the force and joining the anti-government protests that were to convulse the tiny Gulf island kingdom for months.
For the next month, Mr Ghanami spoke openly at rallies against the government of King Hamad bin Isa Al Khalifa.
Bahrain is ruled by the Al Khalifas, a Sunni Muslim royal family. The majority of the indigenous population are Shia Muslims. The Shia, who made up most of the protesters, have complained for years about discrimination in jobs, housing and education.
When GCC forces led by troops from Saudi Arabia entered the kingdom in March, Mr Ghanami, a Shia, went into hiding.
After six weeks on the run, he was arrested. He has been detained in solitary confinement since September.
On Monday he was sentenced to seven and a half years for taking part in 11 rallies and for absence without leave, three years for incitement to hatred against the government and two years for disturbing the peace.
A human rights activist who did not want to be named told the BBC the severity of the sentence reflected official anger.
” He was the first,” the activist said “and he encouraged other officers to quit and join the movement”
The activist claimed that nearly 200 had followed Ali’s lead and joined the protests. All of them were subsequently arrested but only one other received a sentence as long as Mr Ghanami.
Medics’ trial adjourned
Also on Monday, the appeal case involving 20 doctors from Salmaniya hospital was adjourned to March 19.
The doctors had all been convicted and sentenced by a military court in September on a variety of charges related to incidents that occurred in the wake of the clearance of Pearl Roundabout on 17 February.
Doctors at nearby Salmaniya hospital were rounded up, jailed and allegedly tortured into giving confessions before being sentenced to long prison terms.
The doctors said they were only carrying out their professional duties assisting injured people regardless of whether they were protesters or police.
In a claim that has been widely dismissed by international observers as fabricated, the government insisted that doctors had taken over the hospital and were using it as a ‘rebel base’.
Jalila Sayed, a lawyer for one of the doctors told the BBC all the charges should be dismissed and the conviction by the military tribunal overturned.
“The doctors are civilians and should never have been tried in a military court.”
Furthermore she said, the doctors were systematically abused in custody.
“Confessions were obtained under torture and they should never have been allowed as evidence.”
An independent committee of human rights experts, commissioned by King Hamad in an attempt to defuse tensions has already substantially confirmed the torture allegations.
The committee was chaired by a distinguished human rights lawyer Professor Cherif Bassiouni.
King Hamad had accepted the findings of the report when it was delivered to him by Professor Bassiouni in an extraordinary public session in November of last year.
In another case a civilian court examined the conviction by military tribunal of seven men charged with murdering two security officers during the protests. Two were sentenced to death and the others to life imprisonment.
The court today overturned the second stage of the military court process, a decision to reject an appeal by the men. But a lawyer close to the case says the original military court convictions still stand.